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Pneumococcal infections cause serious illness and death among older adults. A capsular polysaccharide vaccine PPSV23 (Pneumovax®) and a conjugated polysaccharide vaccine PCV13 (Prevnar®) are used to prevent these infections, yet underlying responses, and baseline predictors remain unknown. We recruited and vaccinated 39 older adults (>60 years) with PPSV23 or PCV13. Both vaccines induced strong antibody responses at day 28 and similar plasmablast transcriptional signatures at day 10, however, their baseline predictors were distinct. Analyses of baseline flow cytometry and RNA-seq data (bulk and single cell) revealed a novel baseline phenotype that is specifically associated with weaker PCV13 responses, characterized by i) increased expression of cytotoxicity-associated genes and increased CD16+NK frequency; ii) increased Th17 and decreased Th1 cell frequency. Men were more likely to display this cytotoxic phenotype and mounted weaker responses to PCV13 than women. Baseline expression levels of a distinct gene set was predictive of PPSV23 responses. This first precision vaccinology study for pneumococcal vaccine responses of older adults uncovered novel and distinct baseline predictors that might transform vaccination strategies and initiate novel interventions.

Diverse mouse strains have different health and life spans, mimicking the diversity among humans. To capture conserved aging signatures, we studied long-lived C57BL/6J and short-lived NZO/HILtJ mouse strains by profiling transcriptomes and epigenomes of immune cells from peripheral blood and the spleen from young and old mice. Transcriptional activation of the AP-1 transcription factor complex, particularly Fos, Junb, and Jun genes, was the most significant and conserved aging signature across tissues and strains. ATAC-seq data analyses showed that the chromatin around these genes was more accessible with age and there were significantly more binding sites for these TFs with age across all studied tissues, targeting pro-inflammatory molecules including Il6. Age-related increases in binding sites of Jun/Fos factors were also conserved in human peripheral blood ATAC-seq data. Single-cell RNA-seq data from the mouse aging cell atlas Tabula Muris Senis showed that the expression of these genes increased with age in B, T, NK cells, and macrophages, with macrophages from old mice expressing these molecules more abundantly than other cells. Functional data showed that upon myeloid cell activation via poly(I:C), the levels of c-JUN protein and its binding activity increased more significantly in spleen cells from old mice compared to cells from young mice. In addition, upon activation, old cells produced more IL6 compared to young cells. In sum, we showed that the aging-related transcriptional activation of Jun/Fos members of the AP-1 complex is conserved across immune tissues and long- and short-living mouse strains, possibly contributing to increased inflammation with age.

Differences in immune function and responses contribute to health- and life-span disparities between sexes. However, the role of sex in immune system aging is not well understood. Here, we characterize peripheral blood mononuclear cells from 172 healthy adults 22–93 years of age using ATAC-seq, RNA-seq and flow cytometry. These data reveal a shared epigenomic signature of aging including declining naïve T cells and increasing monocyte and cytotoxic cell functions. These changes are greater in magnitude in men and accompanied by a male-specific decline in B-cell-specific loci. Interestingly, genomic differences between sexes increase after age 65, with men having higher innate and pro-inflammatory activity and lower adaptive activity. In a separate cohort (n=39) we studied how older adults respond to two available pneumococcal vaccines: T-dependent Prevnar and T-independent Pneumovax. How older adults respond to these vaccines at the molecular and cellular level, and whether there are pre-vaccination predictors for vaccine responsiveness, is poorly understood. To address this, we characterized serum antibody responses and peripheral blood leukocyte composition using flow cytometry and transcriptional profiles using RNA-seq, in healthy older adults before and after vaccination. The vaccines induced comparable serological responses and increases in the number of ICOS+ T follicular helper cells. A shared plasmablast transcriptional signature (IGHG2, IGHA1, IGHA2) was induced by both vaccines ten days after vaccination, which is distinct from influenza vaccine responses. Importantly, the pre-vaccination (baseline) ratio of Th1/Th17 cells predicted responsiveness to Prevnar but not to Pneumovax. Interestingly, women had higher levels of Th1/Th17; and responded stronger to Prevnar compared to men. This study uncovered how older adults respond to different pneumococcal vaccines and demonstrated the significance of considering biological sex and the immune cell composition for precision vaccinology.

Differences in immune function and responses contribute to health- and life-span disparities between sexes. However, the role of sex in immune system aging is not well understood. Here, we characterize peripheral blood mononuclear cells from 172 healthy adults 22–93 years of age using ATAC-seq, RNA-seq, and flow cytometry. These data reveal a shared epigenomic signature of aging including declining naïve T cell and increasing monocyte and cytotoxic cell functions. These changes are greater in magnitude in men and accompanied by a male-specific decline in B-cell specific loci. Age-related epigenomic changes first spike around late-thirties with similar timing and magnitude between sexes, whereas the second spike is earlier and stronger in men. Unexpectedly, genomic differences between sexes increase after age 65, with men having higher innate and pro-inflammatory activity and lower adaptive activity. Impact of age and sex on immune phenotypes can be visualized at https://immune-aging.jax.org to provide insights into future studies., Whether the immune system aging differs between men and women is barely known. Here the authors characterize gene expression, chromatin state and immune subset composition in the blood of healthy humans 22 to 93 years of age, uncovering shared as well as sex-unique alterations, and create a web resource to interactively explore the data.

Detecting multiplets in single nucleus (sn)ATAC-seq data is challenging due to data sparsity and limited dynamic range. AMULET (ATAC-seq MULtiplet Estimation Tool) enumerates regions with greater than two uniquely aligned reads across the genome to effectively detect multiplets. We evaluate the method by generating snATAC-seq data in the human blood and pancreatic islet samples. AMULET has high precision, estimated via donor-based multiplexing, and high recall, estimated via simulated multiplets, compared to alternatives and identifies multiplets most effectively when a certain read depth of 25K median valid reads per nucleus is achieved. Supplementary Information The online version contains supplementary material available at 10.1186/s13059-021-02469-x.

Increased inflammation with age (i.e., inflammaging) is a hallmark of aging conserved in human and mice, but the underlying mechanisms are poorly understood, partially because a systematic comparative study of mouse and human immune system aging is lacking. We uncovered epigenomic/transcriptomic signatures of aging in spleen and peripheral blood lymphocytes from young (3 months) and old (18 months) mice in two strains: C57BL/6J (long-lived) and NZO/HILtJ (short-lived) and compared these to the aging signatures of human peripheral blood cells. The most predominant and conserved genomic signature of aging in human and mice tissues studied here was the epigenetic activation of several AP-1 complex members (Fos, Fosl2, Junb, Jund). Footprinting analyses showed that these transcription factors ‘bind’ more frequently with age and target pro-inflammatory and effector molecules, including the pro-inflammatory Il6. Analysis of single cell RNA-seq data from the mouse aging cell atlas (Tabula Muris Senis) revealed that AP-1 activation with age is a common feature across all immune cell types within spleens, yet macrophages express these molecules more often than other cells. Functional assays confirmed that spleen cells from older animals have increased c-JUN protein binding and increased IL6 production upon myeloid cell activation using poly(I:C) via TLR3. Western blot data revealed that c-JUN activation with age is not post-transcriptional since its phosphorylation levels were similar between young and old mice. Together, these data established that Jun and Fos families in the AP-1 complex are transcriptionally activated with age and target pro-inflammatory molecules and aging-related increases in the binding of these proteins likely modulate increased inflammation with age.

Similar to other droplet-based single cell assays, single nucleus ATAC-seq (snATAC-seq) data harbor multiplets that confound downstream analyses. Detecting multiplets in snATAC-seq data is particularly challenging due to its sparsity and trinary nature (0 reads: closed chromatin, 1: open in one allele, 2: open in both alleles), yet offers a unique opportunity to infer multiplets when >2 uniquely aligned reads are observed at multiple loci. Here, we implemented the first read count-based multiplet detection method, ATAC-DoubletDetector, that detects multiplets independently of cell-type. Using PBMC and pancreatic islet datasets, ATAC-DoubletDetector captured simulated heterotypic multiplets (different cell-types) with ∼0.60 recall, showing ∼24% improvement over state of the art. ATAC-DoubletDetector detected homotypic multiplets with ∼0.61 recall, representing the first method to detect multiplets originating from the same cell type. Using our novel clustering-based algorithm, multiplets were annotated to their cellular origins with ∼85% accuracy. Application of ATAC-DoubletDetector will improve downstream analysis of snATAC-seq.

Ageing is associated with re-modelling of the immune system to enable the maintenance of life-long immunity. In the CD8(+) T cell compartment, ageing results in the expansion of highly-differentiated cells that exhibit characteristics of cellular senescence. Here we found that CD27(−)CD28(−)CD8(+) T lost the signalling activity of the T cell antigen receptor (TCR) and expressed a protein complex containing the agonistic NK receptor NKG2D and the NK adaptor molecule DAP12, which promoted cytotoxicity against cells that expressed NKG2D ligands. Immunoprecipitation and imaging cytometry indicated that the NKG2D-DAP12 complex was associated with sestrin 2. The genetic inhibition of sestrin 2 resulted in decreased expression of NKG2D and DAP12 and restored TCR signaling in senescent-like CD27(−)CD28(−)CD8(+) T cells. Therefore, during ageing, sestrins induces the reprogramming of non-proliferative senescent-like CD27(−)CD28(−)CD8(+) T cells to acquire a broad-spectrum, innate-like killing activity.

Patients with systemic lupus erythematosus (SLE) display a complex blood transcriptome whose cellular origin is poorly resolved. Using single-cell RNA sequencing, we profiled ~276,000 peripheral blood mononuclear cells from 33 children with SLE with different degrees of disease activity and 11 matched controls. Increased expression of interferon-stimulated genes (ISGs) distinguished cells from children with SLE from healthy control cells. The high ISG expression signature (ISGhi) derived from a small number of transcriptionally defined subpopulations within major cell types, including monocytes, CD4+ and CD8+ T cells, natural killer cells, conventional and plasmacytoid dendritic cells, B cells and especially plasma cells. Expansion of unique subpopulations enriched in ISGs and/or in monogenic lupus-associated genes classified patients with the highest disease activity. Profiling of ~82,000 single peripheral blood mononuclear cells from adults with SLE confirmed the expansion of similar subpopulations in patients with the highest disease activity. This study lays the groundwork for resolving the origin of the SLE transcriptional signatures and the disease heterogeneity towards precision medicine applications. Banchereau and colleagues provide a resource dataset that examines disease-related transcriptional profiles of peripheral whole-blood cells from adolescent patients with SLE by single-cell RNA-seq analysis.

Ucar et al. describe a novel chromatin accessibility signature of aging that is borne by memory CD8+ T cells but is detectable from PBMCs. This signature harbors the IL7R gene as a potential biomarker of aging-associated immunodeficiency., Aging is linked to deficiencies in immune responses and increased systemic inflammation. To unravel the regulatory programs behind these changes, we applied systems immunology approaches and profiled chromatin accessibility and the transcriptome in PBMCs and purified monocytes, B cells, and T cells. Analysis of samples from 77 young and elderly donors revealed a novel and robust aging signature in PBMCs, with simultaneous systematic chromatin closing at promoters and enhancers associated with T cell signaling and a potentially stochastic chromatin opening mostly found at quiescent and repressed sites. Combined analyses of chromatin accessibility and the transcriptome uncovered immune molecules activated/inactivated with aging and identified the silencing of the IL7R gene and the IL-7 signaling pathway genes as potential biomarkers. This signature is borne by memory CD8+ T cells, which exhibited an aging-related loss in binding of NF-κB and STAT factors. Thus, our study provides a unique and comprehensive approach to identifying candidate biomarkers and provides mechanistic insights into aging-associated immunodeficiency.

Alternative splicing (AS) is a key mechanism of biological diversity in eukaryotes allowing a single gene to generate multiple mRNA transcript isoforms, yielding unique proteins that may have distinct or opposing functions. Alterations in AS have been associated with numerous diseases. SLE patients display autoantibodies to components of the spliceosome, chiefly anti-Sm/RNP, anti-Ro/La, and anti-dsDNA. We performed Long-Read sequencing using Pacific Biosciences equipment (LR-Seq), as well as short read RNA-Seq, from adolescent SLE patients’ and healthy controls’ PBMCs, to discover and quantitate splice junctions. A computational pipeline was built to differentially quantify splice junctions in the LR-Seq sequenced isoforms, both known and novel using rMATS (Multivariate Analysis of Transcript Splicing). Compared to Gencode, LR-Seq revealed ~9000 novel transcript isoforms. 55% of all transcripts were expressed in 2 or more samples. A majority of these transcripts belonged to genes associated with cell cycle, metabolism, and inflammation. Additionally, we interrogated our SLE LR-Seq generated transcriptome with publicly available RNA-Seq data from adult SLE and healthy donors. We observed 250 differential expression of exon skipping (ES) splice junctions in transcript isoforms of genes, a majority of which did not exhibit any significant change in gene expression. Of the 250 ES transcript isoforms, 160 exon inclusion events were observed in SLE PBMCs. Fifty percent of the exon inclusion events were found to be in novel transcript isoforms. Thus LR-Seq, besides revealing novel transcripts, allows us to study changes in transcript isoform expression.

In this review, we focused on our studies of cancer dormancy in a murine B cell lymphoma and human breast cancer. Lifelong dormancy was induced in syngeneic mice by prior immunization to the idiotype of the tumor cell (TC) Ig before TC challenge. The mice maintained approximately 10 6 lymphoma cells in their spleen throughout their lifetime despite replication of the TCs at a reduced rate. Recurrences occurred randomly. Because of the balance between replication and cell death, we hypothesized that a similar balance might occur in long-term survivors of breast cancer when the risk of recurrences is very low. We developed a sensitive assay for circulating tumor cells (CTCs) which none were found in normal age-matched women. One third of patients, 7-22 years after mastectomy and without any evidence of disease, had CTCs. The half-life of these CTCs could be deduced from other studies as probably 2-3 hours. Hence, there was a precise balance between replication of TCs (presumably from micrometastases) and cell death. Therefore, a major population of clinically cured breast cancer patients have a chronic disease controlled by their own physiological mechanisms. We speculate on underlying mechanisms based both on studies in experimental models and clinical trials.

The oncogenic activity of the overexpressed HER2 tyrosine kinase receptor requires its localization in the plasma membrane. The antitumor effect of anti-HER2 antibodies (Abs) is mainly dependent on receptor downregulation and comprises p27Kip1-mediated G1 cell cycle arrest. However, one major limitation of anti-HER2 therapy is the reversibility of tumor growth inhibition after discontinuation of treatment caused by the mitogenic signaling associated with cell surface receptor re-expression. We found that the level of p27Kip1 upregulation, inhibition of Cdk2 activity and magnitude of G1 arrest induced by the humanized Ab trastuzumab (Herceptin, HCT) on BT474 and SKBr3 HER2-overexpressing breast cancer cells correlates with the level of cell surface receptor. Thus, continuous exposure of cells to HCT for 72 hr results in downregulation of the cell surface receptor and a concurrent increase in the level of p27Kip1 protein. Discontinuation of Ab exposure after the first 8 hr results in failure to upregulate p27Kip1 and arrest of cell cycle progression. We show that the lysosomotropic amine chloroquine (CQ) augments receptor internalization in HER2-overexpressing cells either pretreated or continuously treated with HCT and leads to an increased and sustained inhibitory effect. The enhanced CQ-dependent loss of functional HER2 from the cell surface resulted in sustained inactivation of the serine/threonine kinase Akt, upregulation of p27Kip1 protein and inhibition of cyclin E/Cdk2 activity. Potentiation of the inhibitory effect of HCT by CQ was directly related to loss of HER2 from the plasma membrane since prevention of Ab-mediated receptor endocytosis by engagement of the receptor with immobilized HCT abrogated the effect of CQ. © 2004 Wiley-Liss, Inc.

A B cell lymphoma model of dormancy in mice was established by prior immunization to the B cell membrane immunoglobulin idiotype. The antibody to the idiotype was the major factor in inducing and maintaining dormancy and acted primarily as an agonist rather than via effector functions. CD8+ T cells synergized with anti-Id in inducing dormancy by secreting IFN-gamma. Cycling in the dormant population was reduced 3-5 fold, but each mouse contained approximately 10(6) tumor cells in its spleen, some of which were cycling, during the 1.5 years of observation. Thus, replication is balanced by cell death.

We show that anti-IgM-induced cell death in a human B lymphoma cell line, B104, is associated with early intracellular acidification and cell shrinkage. In contrast, another human B cell lymphoma line, Daudi, less susceptible to B cell antigen receptor-mediated cell death, responded to anti-IgM with an early increase in intracellular pH (pHi). The anti-IgM-induced changes of pHiwere associated with different levels of activation of the Na+/H+exchanger isoform 1 (NHE1) as judged by its phosphorylation status. Prevention of anti-IgM-induced cell death in B104 cells by the calcineurin phosphatase inhibitor, cyclosporin A, abrogated both intracellular acidification and cell shrinkage and was associated with an increase in the phosphorylation level of NHE1 within the first 60 min of stimulation. This indicates a key role for calcineurin in regulating pHiand cell viability. The potential role of pHiin cell viability was confirmed in Daudi cells treated with an Na+/H+exchanger inhibitor 5-(N,N-hexamethylene)amiloride. These observations indicate that the outcome of the anti-IgM treatment depends on NHE1-controlled pHi. We suggest that inactivation of the NHE1 in anti-IgM-stimulated cells results in intracellular acidification and subsequently triggers or amplifies cell death.

The p21WAF1(p21) cyclin-dependent kinase inhibitor plays a major role in regulating cell cycle arrest. It was recently reported that the p53-independent elevation of p21 protein levels is essential in mediating the G1arrest resulting from signal transduction events initiated by the crosslinking of membrane IgM on Daudi Burkitt lymphoma cells. Although the role of p21 in cell cycle regulation is well documented, there is little information concerning its role in antibody-mediated apoptosis. In the present study, we examined the involvement of p21 in the regulation of apoptosis by suppressing its induction in anti-IgM-treated Daudi cells through a p21 antisense expression construct approach. Reduction in induced p21 protein levels resulted in diminished G1arrest and increased apoptosis. The increased susceptibility to anti-IgM-mediated apoptosis was associated with increased caspase-3-like activity and poly-(ADP)ribose polymerase cleavage. These data suggest that p21 may directly interfere with the caspase cascade, thus playing a dual role in regulating both cell cycle progression and apoptosis.

The majority of BALB/c mice immunized with the BCL1 lymphoma-derived idiotype (Id+) IgM and subsequently challenged with BCL1 tumor cells develop a state of tumor dormancy. The vast majority of dormant lymphoma cells are in cell cycle arrest, but there are also residual replicating cells. In the present studies, we attempted to define features of both the dormant lymphoma cells and the host that lead to escape from dormancy. Escape from dormancy occurs at a steady rate over a 2-year period, suggesting that it is a stochastic process. We found that, in the majority of mice, escape was due to the emergence of genetic variants that were no longer susceptible to the anti-Id–mediated induction of dormancy. Ten percent of these variants were Id−; the remainder were Id+ but could grow in the presence of anti-Id antibodies, suggesting that there were mutations in molecules involved in one or more mIg-mediated negative-signaling pathways. In two of five such escapees, alterations in either Syk, HS1, and/or Lyn were observed. In a small percentage of mice, a low titer of circulating anti-Id antibody before tumor challenge correlated with a subsequent, more rapid loss of dormancy.

Tumor dormancy can be induced in a murine B cell lymphoma (BCL1) by immunizing BALB/c mice with the tumor immunoglobulin (Ig) before tumor cell challenge. In this report, we have investigated the immunological and cellular mechanisms underlying the induction of dormancy. BCL1 tumor cells were injected into SCID mice passively immunized with antibody against different epitopes on IgM or IgD with or without idiotype (Id)-immune T lymphocytes. Results indicate that antibody to IgM is sufficient to induce a state of dormancy. Antibodies against other cell surface molecules including IgD and CD44 (Pgp1) had no effect on tumor growth. Id-immune T cells by themselves also had no effect on tumor growth in SCID mice. However, simultaneous transfer of anti-Id and Id-immune T cells enhanced both the induction and duration of the dormant state. In vitro studies indicated that antibody to IgM induced apoptosis within several hours and cell cycle arrest by 24 h. Hyper cross-linking increased apoptosis. The Fc gamma RII receptor played little or no role in the negative signaling. Antibodies that did not negatively signal in vitro did not induce dormancy in vivo. The results suggest that anti-IgM plays a decisive role in inducing tumor dormancy to BCL1 by acting as an agonist of IgM-mediated signal transduction pathways.

CD22 is broadly expressed on human B cell lymphomas. Monoclonal anti-CD22 antibodies alone, or coupled to toxins, have been used to selectively target these tumors both in SCID mice with xenografted human lymphoma cell lines and in patients with B cell lymphomas. Single-walled carbon nanotubes (CNTs) attached to antibodies or peptides represent another approach to targeting cancer cells. CNTs convert absorbed near-infrared (NIR) light to heat, which can thermally ablate cells that have bound the CNTs. We have previously demonstrated that monoclonal antibodies (MAbs) noncovalently coupled to CNTs can specifically target and kill cells in vitro. Here, we describe the preparation of conjugates in which the MAbs are covalently conjugated to the CNTs. The specificity of both the binding and NIR-mediated killing of the tumor cells by the MAb-CNTs is demonstrated by using CD22+CD25− Daudi cells, CD22−CD25+ phytohemagglutinin-activated normal human peripheral blood mononuclear cells, and CNTs covalently modified with either anti-CD22 or anti-CD25. We further demonstrate that the stability and specificity of the MAb-CNT conjugates are preserved following incubation in either sodium dodecyl sulfate or mouse serum, indicating that they should be stable for in vivo use. © 2009 UICC

The current antitumor strategies, including chemotherapy, radiotherapy, naked and/or conjugated monoclonal antibody (MAb) therapy or combinations of these have major limitations ranging from insufficient cytotoxicity to severe side effects. A potential solution is the use of targeted nanoparticles such as carbon nanotubes (CNTs). CNTs have been demonstrated to possess unique properties including the ability to emit heat when exposed to either near-infrared (NIR) light. The proposal test the possibility to use targeted CNTs to selectively ablate tumors by the local heat generated by cell-bound CNTs under NIR light exposure. The present study describes the preparation of conjugates with MAbs indirectly or directly coupled to CNTs and the characterization of the chemical and biological properties of the resulting MAb-CNT conjugates. We, thus, prepared MAb-CNT conjugates with stable chemical structure. The CNTs preserved the key spectral properties, are not toxic and are stable in physiological buffers. They show a high tumor cell specificity and selective thermal depletion of tumor cells in cultures or in mouse models. This study will test the hypothesis that chemically stable nanoparticles, such as CNTs, might represent an alternative strategy to the current antitumor agents and provide a proof-of-principle for the therapy of at least a number of skin tumors.

Single-walled carbon nanotubes (CNTs) emit heat when they absorb energy from near-infrared (NIR) light. Tissue is relatively transparent to NIR, which suggests that targeting CNTs to tumor cells, followed by noninvasive exposure to NIR light, will ablate tumors within the range of NIR. In this study, we demonstrate the specific binding of antibody-coupled CNTs to tumor cells in vitro , followed by their highly specific ablation with NIR light. Biotinylated polar lipids were used to prepare stable, biocompatible, noncytotoxic CNT dispersions that were then attached to one of two different neutralite avidin-derivatized mAbs directed against either human CD22 or CD25. CD22 + CD25 − Daudi cells bound only CNTs coupled to the anti-CD22 mAb; CD22 − CD25 + activated peripheral blood mononuclear cells bound only to the CNTs coupled to the anti-CD25 mAb. Most importantly, only the specifically targeted cells were killed after exposure to NIR light.

We formulate models of the mechanism(s) by which B cell lymphoma cells stimulated with an antibody specific to the B cell receptor (IgM) become quiescent or apoptotic. In particular, we aim to reproduce experimental results by Marches et al. according to which the fate of the targeted cells (Daudi) depends on the levels of expression of p 21 Waf 1 (p21) cell-cycle inhibitor. A simple model is formulated in which the basic ingredients are p21 and caspase activity, and their mutual inhibition. We show that this model does not reproduce the experimental results and that further refinement is needed. A second model successfully reproduces the experimental observations, for a given set of parameter values, indicating a critical role for Myc in the fate decision process. We use bifurcation analysis and objective sensitivity analysis to assess the robustness of our results. Importantly, this analysis yields experimentally testable predictions on the role of Myc, which could have therapeutic implications.

We have previously demonstrated that an anti-CD19 monoclonal antibody (MAb; HD37) inhibits the function of the P-glycoprotein (P-gp) pump in a multidrug-resistant (MDR) B-lymphoma cell line, Namalwa/MDR1, and that this effect is not due to the recognition of a cross-reactive epitope on P-gp. In this study, we have used the same cell line to define the mechanisms responsible for the effect of HD37 on the P-gp pump. Using fluorescence resonance energy transfer (FRET), we show that CD19 and P-gp are constitutively associated in cells. In the absence of treatment with anti-CD19, 40% of P-gp molecules expressed by Namalwa/MDR1 cells reside in the low-density lipid (ie, cholesterol-rich) microdomains (lipid rafts). Following treatment of the cells with HD37 and disruption of the interactions between P-gp and CD19, P-gp translocated out of lipid rafts and CD19 translocated into lipid rafts. The effect of chemosensitization on Namalwa/MDR1 cells was specific for CD19; an anti-CD22 MAb had no such effect, although the cells express CD22. These results suggest that anti-CD19 might chemosensitize P-gp+ cells by interfering with interactions between CD19 and P-gp, rapidly resulting in the translocation of P-gp into a compartment on the plasma membrane where it is no longer active.

Her-2 (p185(erbB-2)) is a transmembrane tyrosine kinase receptor, which is encoded by the Her-2/neu proto-oncogene. Her-2 is overexpressed on 30% of highly malignant breast cancers. Monoclonal antibodies (MAbs) against Her-2 inhibit the growth of Her-2-overexpressing tumor cells and this occurs by a variety of mechanisms. One such MAb, Herceptin (Trastuzumab), has been approved for human use. We have generated a panel of murine anti-Her-2 MAbs against nine different epitopes on the extracellular domain of Her-2 and have evaluated the antitumor activity of three of these MAbs alone and in combination, both in vitro and in vivo. We found that MAbs (against different epitopes) make a highly effective mixture, which was more effective than the individual MAbs in treating s.c. tumor nodules of BT474 cells in SCID mice. In vitro, the MAb mixture was also more effective than the single MAbs in inducing antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, inhibiting cell growth and inducing apoptosis, and inhibiting the secretion of vascular endothelial growth factor. Taken together, these activities might explain the superior performance of the MAb mixture in vivo.

Cancer dormancy is a phenomenon where neoplastic cells exist within a host without progressive growth (1–3). Clinical examples of dormancy in humans can be found in cases of melanoma (4, 5), breast carcinoma (6), and lymphoma [R. Levy personal communication]. To identify potential mechanisms regulating cancer dormancy, a murine lymphoma model has been established. This dormancy model system utilizes a mouse B-cell lymphoma, BCL1, whose aggressive growth normally leads to rapid splenomegaly, late onset leukemia, and eventual death within 30 days after challenge. However, the development of splenomegaly and subsequent disease can be prevented by immunization of syngeneic recipients with membrane immunoglobulin (mlg) purified from BCL1, prior to challenge. Seventy percent of immunized animals do not develop tumor by 60 days and in some cases can survive up to 2 years, the lifespan of a normal animal. Dormancy established in these animals is not simply the elimination of BCL1 by the host immune system because BCL1, can be specifically detected using polymerase chain reaction and can be isolated using flow cytometry from the spleen of dormant animals. Adoptive transfer of splenocytes from dormant animals to naive recipients results in regrowth of the tumor (7), and is further evidence that BCL1, cells are present.

Signal transduction initiated by crosslinking of antigen-specific receptors on T- and B-lymphoma cells induces apoptosis. In T-lymphoma cells, such crosslinking results in upregulation of the APO-1 ligand, which then interacts with induced or constitutively expressed APO-1, thereby triggering apoptosis. Here we show that crosslinking the membrane immunoglobulin on human lymphoma cells (Daudi) (that constitutively express APO-1) does not induce synthesis of APO-1 ligand. Further, a noncytotoxic fragment of anti-APO-1 antibody that blocks T-cell-receptor-mediated apoptosis in T-lymphoma cells does not block anti-mu-induced apoptosis. Hence, in B-lymphoma cells, apoptosis induced by signaling via membrane IgM is not mediated by the APO-1 ligand.

Cancer dormancy is a well-recognized clinical phenomenon in which tumor cells are present, but the tumor burden does not increase for long periods of time1–3. However, tumor cells can regrow many years later. In breast cancer, there is a steady rate of recurrence 10 to 20 years after removal of the primary tumorl3,4 and the recurrent tumor frequently grows at a rapid rate(5). A particularly pertinent example is the low grade (follicular) form of non-Hodgkin’s lymphoma (NHL) in which long-term remissions are common but, eventually, virtually all die of a recurrence. Levy and Miller(5) have treated such patients with monoclonal anti-idiotype (Id) and have achieved remissions in a high proportion of patients. Relapses, many caused by Id-negative variants, are frequent indicating that the antibody (Ab) was particularly effective in inducing dormancy in cells bearing the corresponding idiotope but that hypermutation of VH and VL genes eventually allow some tumor cells from the original clone to escape(5–7).

Single-walled carbon nanotubes (CNTs) convert absorbed near infrared (NIR) light into heat. The use of CNTs in the NIR-mediated photothermal ablation of tumor cells is attractive because the penetration of NIR light through normal tissues is optimal and the side effects are minimal. Targeted thermal ablation with minimal collateral damage can be achieved by using CNTs attached to tumor-specific monoclonal antibodies (MAbs). However, the role that the cellular internalization of CNTs plays in the subsequent sensitivity of the target cells to NIR-mediated photothermal ablation remains undefined. To address this issue, we used CNTs covalently coupled to an anti-Her2 or a control MAb and tested their ability to bind, internalize, and photothermally ablate Her2(+) but not Her2(-) breast cancer cell lines. Using flow cytometry, immunofluorescence, and confocal Raman microscopy, we observed the gradual time-dependent receptor-mediated endocytosis of anti-Her2-CNTs whereas a control MAb-CNT conjugate did not bind to the cells. Most importantly, the Her2(+) cells that internalized the MAb-CNTs were more sensitive to NIR-mediated photothermal damage than cells that could bind to, but not internalize the MAb-CNTs. These results suggest that both the targeting and internalization of MAb-CNTs might result in the most effective thermal ablation of tumor cells following their exposure to NIR light.