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Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematologic malignancies or inherited disorders. Ex vivo T-cell depletion (TCD) of the graft and post-transplantation immunosuppression efficiently prevent the development of graft-versus-host disease (GVHD). However, the consequence of these nonspecific approaches is a long-lasting immunodeficiency associated with increased disease relapse, graft rejection, and reactivation of viral infections. Donor lymphocyte infusion, to treat leukemic relapse after allogeneic HSCT, can cause severe GVHD. Several strategies are being optimized to specifically inactivate anti-host T cells while preserving antileukemic or antimicrobial immunocompetence, based on ex vivo or in vivo elimination of anti-host T cells or on the modulation of their anti-host activity., (Copyright 2002 by W.B. Saunders Company.)

The success of HSCT from HLA partially disparate donors depends on the development of new strategies able to efficiently prevent GVHD and to protect patients from infections and relapse. Using an immunotoxin (IT) directed against the alpha-chain (p55) of the human IL-2r (RFT5-SMPT-dgA), we have previously shown that it is possible to kill mature T cells activated towards a specific HLA complex by a one-way MLR. We designed a clinical trial assessing the effect of infusing increasing doses of T lymphocytes in the setting of children recipients of non HLA genetically identical HSCT. Thirteen patients have been enrolled from September 1998 to April 2000 and fourteen HSCT have been realized in 13 patients (pts). Donors were MUD in 3 cases and familial HLA partially disparate in the remaining cases. Allodepleted donor T cells were injected between day +14 and day +30 provided that ATG was undetectable in the serum and blood PMN counts was > 500/microliter. The mean age of these patients was 17 months (range 1 to 42). Diagnosis included immune deficient and malignant hemopathies. Three patients received 1 x 10(5) allodepleted T cell/kg, 7 patients received 4 x 10(5)/kg and 4 patients received 6 x 10(5)/kg allodepleted T cells. Full inhibition of MLR was achieved in 12 out of 14 cases. In two cases, a residual T cell reactivity to the recipient was observed (4 to 5%) and patients developed grade II aGVHD. aGVHD occurred in 4 out of 11 grafted patients (all grade II). No chronic GVHD has developed, so far. Three patients died from severe VOD or PHT at day +34, day 51 and day +166, while one infected patient by VZV, CMV and EBV before HSCT died 6 months after transplantation from meningoencephalitis and another patient died from relapse at day +291. The patient for which there was no engraftment died at day +48 from staphylococcus infection. Overall survival is 54%, with a median follow up of 8 months; the mean time to reach a blood lymphocyte count > 500 was 41 days, to reach a CD3 count > 300 microliters 63 days (20-111), CD4 > 200 microliters 97 days and positive mitogen-induced proliferation 90 days. In three patients, a tetanus-toxoid positive proliferation was detected before immunization. From this intermediate analysis, we conclude that 1) specific allodepletion is an effective approach to prevent aGVHD in a haploincompatible setting, 2) data on immunological reconstitution suggest that infused T cells do survive and expand. A higher number of patients must be enrolled to determine the optimal number of T cells to infuse.

Insulin-dependent diabetes mellitus (IDDM) is not a disease of unbridled destruction. The autoimmune attack on pancreatic beta cells has two distinct stages - insulitis and diabetes - and progression of the former to the latter appears to be highly regulated. Identifying the factors controlling this transition has been difficult because it is a complex process that occurs non-universally and asynchronously. We have overcome these difficulties by coupling a simplified TCR transgenic (tg) model of IDDM and the immunosuppressive drug cyclophosphamide (CY). Young BDC2.5 TCR tg mice show insulitis but not diabetes; CY treatment provoked diabetes in 100% of animals with rapid, highly reproducible kinetics. This allowed a detailed temporal analysis of changes in cellular organization and cytokine gene expression within the lesion. The monokines IL-18, IL-12 and TNF-alpha were pivotal, their induction occurring almost immediately and their coordinate action being required for the onset of aggression. Other cytokines with direct toxicity for beta cells, including IL-1 -beta, IL-6 and IFN-gamma, were subsequently induced; in contrast, there was no cellular or molecular evidence of cell contact-mediated mechanisms of beta cell death.