Selective depletion of donor alloreactive T cells without loss of antiviral or antileukemic responses

Abstract

Poor immune reconstitution after haploidentical stem cell transplantation results in a high mortality from viral infections and relapse. One approach to overcome this problem is to selectively deplete the graft of alloreactive cells using an immunotoxin directed against the activation marker CD25. However, the degree of depletion of alloreactive cells is variable following stimulation with recipient peripheral blood mononuclear cells (PBMCs), and this can result in graft versus host disease (GVHD). We have refined this approach using recipient Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) as stimulators to activate donor alloreactive T cells. Our studies demonstrate that allodepletion with an anti-CD25 immunotoxin following stimulation with HLA-mismatched host LCLs more consistently depleted in vitro alloreactivity than stimulation with host PBMCs, as assessed in primary mixed lymphocyte reactions (MLRs). Allodepletion using this approach specifically abrogates cytotoxic T-cell responses against host LCLs. In interferon-␥ (IFN-␥) enzymelinked immunospot (ELISPOT) assays, antiviral responses to adenovirus and cytomegalovirus (CMV) were preserved following allodepletion. Likewise, using HLA-A2-pp65 tetramers, we have shown that the frequency of CMV-specific T cells is unaffected by allodepletion. Moreover, the donor anti-EBV response is partially retained by recognition of EBV antigens through the nonshared haplotype. Finally, we studied whether allodepletion affects the response to candidate tumor antigens in myeloid malignancies. Using HLA-A2-PR1 tetramer analysis, we found that the frequency of T cells recognizing the PR1 epitope of proteinase 3 was not significantly different in allodepleted and unmanipulated PBMCs from patients with chronic myeloid leukemia (CML) undergoing transplantation. Based on these data, we have embarked on a phase 1 clinical trial of addback of allo-LCL-depleted donor T cells in the haplo-identical setting.

Membrane-bound CD95 ligand expressed on human antigen-presenting cells prevents alloantigen-specific T cell response without impairment of viral and third-party T cell immunity

“…LCL used as APC are highly efficient in activation of T cells 39 and are available in unlimited numbers. However, death ligand expressing LCL might abrogate T cell responses to minor antigens including tumor antigens restricted to the hematopoetic system in situations when antitumor responses are required for therapy.…”

Inducible caspase-9 suicide gene controls adverse effects from alloreplete T cells after haploidentical stem cell transplantation

“…[1][2][3] Removal of all T cells increases the risk of graft rejection, relapse, and viral and other opportunistic infections. [4][5][6] Consequently, efforts have been made to retain the desired T-cell subsets while selectively depleting alloreactive T cells [7][8][9] or enriching for the cells that are directed to pathogens or malignancies, or that are enriched for GVHD-suppressive regulatory T cells. [10][11][12] Although each of these strategies is feasible, it is difficult to develop a single T-cell manipulation that both eliminates alloreactivity and spares T cells representing all the available antiviral and antitumor specificities in the donor's peripheral blood (PB).…”

Outcome of alloanergized haploidentical bone marrow transplantation after ex vivo costimulatory blockade: results of 2 phase 1 studies

“…Most of these approaches use a common mechanistic platform of ex vivo donor T-cell stimulation by recipient alloantigens and subsequent removal or destruction of alloreactive T cells, identified by expression of activation markers, proliferation, or metabolic activity. [8][9][10][11][12] An alternative to selective allodepletion is induction of allospecific anergy (hyporesponsiveness to subsequent restimulation with alloantigens) in donor T cells before HSCT. T cells require at least 2 signals to become activated: cognate antigen/ MHC binding to the T-cell receptor (signal 1) and positive costimulatory signals from antigen presenting cells (APCs; signal 2).…”