A Radiation-Free Immune and Epigenetics Based Conditioning Regimen for Allogeneic HCT: Combination of Anti-CD3 and Romidepsin.

Hematopoietic cell transplantation (HCT) is a curative therapy for hematological malignancies as well as refractory autoimmune diseases. However, graft versus host disease (GVHD) remains a major obstacle in classical HCT, where recipients are usually conditioned with total body irradiation or high dose chemotherapy. We recently reported that donor CD8⁺ T cells facilitated engraftment and mediated graft versus leukemia (GVL) without causing graft versus host disease (GVHD) in young (6–8 weeks old) MHC-mismatched mouse recipients conditioned with anti-CD3 mAb (Blood 2005). Thereafter, we observed that anti-CD3 conditioning alone was not sufficient for induction of chimerism in old (>12 weeks) recipients, due to the higher percentage of residual host CD8⁺ T cells in the old recipients. Romidepsin (Desipeptide), a histone deacetylase inhibitor, was reported to induce apoptosis of human T cell lymphoma lines. We hypothesize that depsipeptide will induce the apoptosis of anti-CD3 activated proliferating T cells, and that conditioning with a combination of anti-CD3 and depsipeptide will markedly reduce the residual host T cells and allow donor stem cell engraftment.

To test our hypothesis, we first added Romidepsin (1.25–10 ng/ml) to cultures of T cells with or without anti-CD3 stimulation. We found that, although Romidepsin showed no effect on un-stimulated T cells, it augmented apoptosis of anti-CD3 activated T cells in a dose dependent manner, and the maximum augmentation was 5 fold. In addition, when Romidepsin (1.25–10 ng/ml) was added to a culture of mixed lymphocyte reaction (MLR), we found that it suppressed MLR in a dose dependent manner also, and the maximum suppression was greater than 98%. Second, old (> 12 weeks) BALB/c recipients were conditioned with one I.V. injection of anti-CD3 (20μg/g) and three I.P. injections (every other day) of Romidepsin at a dose of 0.4 μg/g. 7 days after anti-CD3 injection, recipients were injected with donor bone marrow cells (100×10⁶) and CD4⁺- T depleted spleen (CD4⁻-SPL) cells (100×10⁶). CD4⁻-SPL cells were injected again 7 days later. We found that, 4 weeks after HCT, 7/8 of the recipients conditioned with a combination of anti-CD3 and Romidepsin but only 1/8 of the recipients conditioned with anti-CD3 alone became chimeric. The recipients showed healthy appearance without signs of GVHD. The results are combined from two replicate experiments. This radiation free and GVHD preventive conditioning regimen may provide a novel approach for clinical HCT.