Purified CD4 T Lymphocyte Infusion Can Result in Graft-Versus-Leukemia Reactivity without Gvhd by Recognition of Broadly Expressed Minor Histocompatibility Antigens in HLA Class-II

Abstract 4116

Donor lymphocyte infusion (DLI) after allogeneic stem cell transplantation (alloSCT) can mediate curative Graft-versus-Leukemia (GVL) reactivity although frequently at the cost of Graft-versus-Host Disease (GVHD). We previously illustrated that donor CD8 T lymphocytes recognizing HLA class-I restricted minor histocompatibility antigens (MiHAs) that are broadly expressed on tissues of the recipient cause GVL associated with GVHD, whereas T lymphocytes recognizing MiHAs selectively expressed on hematopoietic cells, including the malignant cells, can selectively mediate GVL without GVHD. Since in contrast to HLA class-I, expression of HLA class-II molecules is predominantly restricted to hematopoietic cells, we hypothesized that infused purified donor CD4 T lymphocytes may selectively recognize and eliminate hematopoietic cells from the recipient resulting in GVL without GVHD.

We treated a patient with CML in blastic phase in remission after intensive chemotherapy with T cell depleted alloSCT from his HLA-identical sibling donor after myelo-ablative conditioning. After donor engraftment, recipient hematopoiesis reoccurred within 3 months to 90% of CD8 T lymphocytes, 13% of CD4 T lymphocytes and 5% of myelopoiesis. As part of a clinical trial, the patient was treated with 10⁶/kg positively selected purified donor derived CD4 T lymphocytes resulting within 19 weeks in conversion into full donor chimerism in all hematopoietic cell lineages in the total absence of GVHD.

To characterize the nature of this hematopoiesis restricted immune response, in vivo activated HLA-DR positive CD4 and CD8 T lymphocytes were clonally isolated by flowcytometric cell sorting at the time of the clinical response, expanded and tested for alloreactivity on patient and donor derived hematopoietic target cells using IFNγ ELISA. From the 204 expanding CD4 T lymphocyte clones 31 clones were alloreactive, whereas none of the 66 expanding CD8 T lymphocyte clones showed alloreactivity.

To further identify the fine specificity of this hematopoiesis directed HLA class-II restricted immune response, target molecules of several T lymphocyte clones were molecularly characterized using whole genome association scanning. We first performed blocking studies with HLA class-II restricted monoclonal antibodies and identified HLA-DR to be the restriction molecule. Next, a large panel of third party EBV-LCLs was retrovirally transduced with each of the possible restriction molecules being HLA-DRB1*11:01, HLA-DRB1*15:01, HLA-DRB3*02:02 and HLA-DRB5*01:01. By comparing the recognition pattern of the transduced EBV-LCLs with the 1.1 million single nucleotide polymorphisms in each EBV-LCL, we identified 3 novel MiHAs. Synthesis and analysis of the patient and donor derived allelic peptide variants further confirmed the specificity of the MiHAs as LB-KHNYN-1K in the context of HLA-DRB5*01:01, LB-CTSB-1G in HLA-DRB1*11:01 and LB-ZDHHC13-1K in HLA-DRB1*15:01. Gene expression profiles of KHNYN (located on chromosome 14), CTSB (chromosome 8) and ZDHHC13 (chromosome 11) illustrated that the genes encoding these MiHAs were not only transcribed in hematopoietic cells, but also in other tissues including GVHD target tissues. These results further illustrated that the hematopoietic specificity of the CD4 T lymphocyte response was mainly defined by the restricted expression of the HLA-DR molecules on hematopoietic cells.

We conclude that purified CD4 DLI can lead to GVL without GVHD by a selective HLA class-II restricted immune response against patient hematopoiesis. By molecular characterization of 3 novel HLA-DR restricted MiHAs we illustrated that the relative specificity of HLA class-II molecules on hematopoietic cells under non inflammatory conditions was probably responsible for this effect. Since HLA class-II is predominantly expressed on hematopoietic cells only, infusion of donor CD4 T lymphocytes under non inflammatory conditions after HLA identical alloSCT can result in efficient induction of GVL without the toxicity of GVHD.