Enrichment of Allogeneic Tumor Antigen-Specific T Cells From Bone Marrow (BM) of Patients Treated with High-Dose Post-Transplant Cyclophoshamide (Cy) – A Novel Approach to Adoptive Immunotherapy

Donor lymphocyte infusions (DLI) has limited efficacy and is associated with substantial graft vs host disease (GVHD) in treating relapse after allogeneic BMT (alloBMT) in large part due to the absence of significant tumor specificity. Thus, novel strategies are required that increase the tumor specificity with reduced alloreactivity. High-dose Cy post-BMT effectively reduces GVHD through early elimination of allo-reactive T cells and enables immune reconstitution free of ongoing pharmacologic immunosuppression. Since the BM is both the site of disease in most hematologic malignancies and a reservoir of tumor specific T cells, we hypothesized that marrow infiltrating lymphocytes (MILs) collected after alloBMT in patients treated with high-dose Cy could be a source of tumor-specific T cells for adoptive immunotherapy.

BM was obtained from patients 2 –12 months after HLA-matched alloBMT on the clinical trial using high-dose post-transplant Cy as a single agent GVHD prophylaxis. The MILs were activated and expanded with CD3/CD28 antibody-coated beads.

Allo-MILs can be reproducibly expanded (574-fold avg expansion; 14–2000) at all time points tested. The activated allo-MILs are not anergic, exhibit anti-HLA-reactivity against third party allo-antigens but do not respond to recipient allo-antigens. Tumor-specific MILs were significantly expanded as determined by reactivity to HL60/K562 myeloid cell lysates (P<0.0001; pre- vs. post-activation). In contrast, no change was observed in cultures pulsed with irrelevant antigens, thus suggesting the specificity of the response. The ability to expand allogeneic antigen-specific MILs was also confirmed with a 15.5 fold expansion of PR-1 specific (HLA) A*0201-restricted CD8⁺ T-cells using tetramers.

We can augment the tumor-specificity of MILs obtained post-transplant with minimal allo-reactivity in patients treated with post-BMT high-dose Cy. This could represent a novel approach to highly tumor-specific DLI. A phase I/II trial is planned to assess the safety and feasibility of administering ex vivo expanded post-transplant, allogeneic MILs to patients with relapsed hematologic malignancies after alloHSCT.

No relevant conflicts of interest to declare.