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Chimeric antigen receptor (CAR) T-cells targeting CD19 demonstrate remarkable efficacy in treating B-lineage acute lymphoblastic leukemia (BL-ALL), yet up to 39% of treated patients relapse with CD19(−) disease. We report that CD19(−) escape is associated with downregulation, but preservation, of targetable expression of CD20 and CD22. Accordingly, we reasoned that broadening the spectrum of CD19CAR T-cells to include both CD20 and CD22 would enable them to target CD19(−) escape BL-ALL while preserving their upfront efficacy. We created a CD19/20/22-targeting CAR T-cell by coexpressing individual CAR molecules on a single T-cell using one tricistronic transgene. CD19/20/22CAR T-cells killed CD19(−) blasts from patients who relapsed after CD19CAR T-cell therapy and CRISPR/Cas9 CD19 knockout primary BL-ALL both in vitro and in an animal model, while CD19CAR T-cells were ineffective. At the subcellular level, CD19/20/22CAR T-cells formed dense immune synapses with target cells that mediated effective cytolytic complex formation, were efficient serial killers in single-cell tracking studies, and were as efficacious as CD19CAR T-cells against primary CD19(+) disease. In conclusion, independent of CD19 expression, CD19/20/22CAR T-cells could be used as salvage or front-line CAR therapy for patients with recalcitrant disease.

Recurrent medulloblastoma and ependymoma are universally lethal, with no approved targeted therapies and few candidates presently under clinical evaluation. Nearly all recurrent medulloblastomas and posterior fossa group A (PFA) ependymomas are located adjacent to and bathed by the cerebrospinal fluid, presenting an opportunity for locoregional therapy, bypassing the blood–brain barrier. We identify three cell-surface targets, EPHA2, HER2 and interleukin 13 receptor α2, expressed on medulloblastomas and ependymomas, but not expressed in the normal developing brain. We validate intrathecal delivery of EPHA2, HER2 and interleukin 13 receptor α2 chimeric antigen receptor T cells as an effective treatment for primary, metastatic and recurrent group 3 medulloblastoma and PFA ependymoma xenografts in mouse models. Finally, we demonstrate that administration of these chimeric antigen receptor T cells into the cerebrospinal fluid, alone or in combination with azacytidine, is a highly effective therapy for multiple metastatic mouse models of group 3 medulloblastoma and PFA ependymoma, thereby providing a rationale for clinical trials of these approaches in humans.

e15586 Background: In Saudi Arabia, the incidence of colorectal cancer has been increased over the past few years. The optimal treatment beyond the second line is not fully understood. To the best of our knowledge, the efficacy and disease outcomes of triflurodine/tipiracil in Saudi patients with refractory metastatic colorectal cancer(mCRC) has not been studied yet. Our study is a real-life practice evaluation of the efficacy of triflurodine/tipiracil in patients with refractory mCRC. Moreover, the prognosis and the prognostic significance of the different clinical variables have been analyzed. Methods: A retrospective, multi-centers ( 5 centers representative of Saudi Arabia )observational study in patients with mCRC who have received triflurodine/tipiracil beyond oxaliplatin & Irinotecan-based chemotherapy between December 2018-December 2020.We aimed to assess the response to triflurodine/tipiracil, to evaluate the progression-free survival (PFS ), the overall survival (OS), and the associated factors of prognostic significance. Results:The data of 100 patients with refractory mCRC who has received triflurodine/tipiracil have been analyzed. The mean age was 55.2 +11.8 years. Forty-two patients were (42%) females and 58 (58%) were male patients. Sigmoid was the most common primary site of cancer in 35 (35%) patients, followed by rectum 29 (29%). Peritoneal metastasis was present in 17 (23.3%) patients ,liver in 51(56.6%) and lung in 39 (50.7%). Metastatic sites were ≥ 2 in 45 (45%) patients. Metastatic lesions were ≥ 5 in 65 (65%) patients. Xelox chemotherapy regimen was the most commonly used first-line chemotherapy which represents 43%, while Folfiri or Xeliri combination was the most used second line in 57 (60%). For the third line, Folfox or Xelox was used in 81 (83.5%) patients. The fourth line was given to 49 (67.1%). For first-line biological agents, Cetuximab was used most frequently 31 (46.3%).Evaluation of the response to treatment with triflurodine/tipiracil revealed one patient (1%) with a complete response,3 patients (3%) with partial response, 28 (28%) patients with stable disease, and 66 (66%) showed progressive disease. The estimated median progression-free survival was 5 months ( 3.839 - 6.161) and the median overall survival was 12 months (9.732-14.268). The log-rank analysis showed that the baseline neutrophils ≤ 75 % ( P-value= 0.0092) and low hemoglobin level (P-value= 0.0245) were strongly associated with a higher survival. By multivariate Cox regression analysis, the neutrophil count ≤ 75 % was the only independent predictor for survival. Conclusions: Trifluridine/tipiracil is effective in patients with refractory mCRC. The low neutrophil count might predict a better overall survival.

3031 Background: Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the immunosuppressive tumor microenvironment. Adoptively transferred CAR T cells remain susceptible to inhibition via the engagement of co-inhibitory receptors on their surface such as PD1, BTLA, CTLA4 and LAG3. The subsequent recruitment of Src homology region 2 containing protein tyrosine phosphatase 2 (SHP2) by these receptors to the immune synapse may represent a common mechanism of T cell inhibition, as SHP2 can de-phosphorylate key signaling molecules that mediate T cell activation (including CD28 and CD3ζ). We hypothesized that SHP2 deletion will simultaneously offset the effects of multiple co-inhibitory receptors, thereby improving the anti-tumor activity of CAR T cells. Methods: Electroporation of sgRNA/Cas9 ribonucleoprotein complexes into human T cells was used to knockout (KO) SHP2. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 endodomain) targeting HER2. The phenotype of wild-type (WT) and SHP2KO CAR T cells was evaluated with mass cytometry and flow cytometry. Their anti-tumor function was tested in vitro using the xCELLigence assay (an impedance-based cytotoxicity assay), and in vivo, in an orthotopic xenograft mouse model of GBM. Results: Efficient and reproducible depletion of the SHP2 protein in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect CAR T cell expansion, proliferation or baseline phenotype. However, following co-culture with HER2+ LN229-GBM cells, the CD8+ central memory (CCR7+ CD45RA-) and effector memory (CCR7- CD45RA-) subsets were enriched to a greater extent in the SHP2KO CAR T cells. The pattern of cytokine co-expression varied between donors in a single-cell analysis comparing SHP2KO to WT CAR T cells after encountering LN229 cells. Functionally, SHP2KO CAR T cells derived from the majority of healthy donor and patient peripheral blood eliminated LN229 cells more rapidly in vitro. In an orthotopic mouse model of GBM, SHP2KO CAR T cells showed better early control of established LN229 xenografts and improved survival in comparison to WT CAR T cells. Conclusions: SHP2 deletion in CD28ζ.CAR T cells improves their anti-tumor activity.

Objective To investigate the true character of the harem conspiracy described in the Judicial Papyrus of Turin and determine whether Ramesses III was indeed killed. Design Anthropological, forensic, radiological, and genetic study of the mummies of Ramesses III and unknown man E, found together and taken from the 20th dynasty of ancient Egypt (circa 1190-1070 BC). Results Computed tomography scans revealed a deep cut in Ramesses III's throat, probably made by a sharp knife. During the mummification process, a Horus eye amulet was inserted in the wound for healing purposes, and the neck was covered by a collar of thick linen layers. Forensic examination of unknown man E showed compressed skin folds around his neck and a thoracic inflation. Unknown man E also had an unusual mummification procedure. According to genetic analyses, both mummies had identical haplotypes of the Y chromosome and a common male lineage. Conclusions This study suggests that Ramesses III was murdered during the harem conspiracy by the cutting of his throat. Unknown man E is a possible candidate as Ramesses III's son Pentawere.