Towards functional transplant donor matching by measurement of granzyme A and granzyme B production levels

Granzyme A-producing T helper cells are critical for acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) can occur after hematopoietic cell transplant in patients undergoing treatment for hematological malignancies or inborn errors. Although CD4+ T helper (Th) cells play a major role in aGVHD, the mechanisms by which they contribute, particularly within the intestines, have remained elusive. We have identified a potentially novel subset of Th cells that accumulated in the intestines and produced the serine protease granzyme A (GrA). GrA+ Th cells were distinct from other Th lineages and exhibited a noncytolytic phenotype. In vitro, GrA+ Th cells differentiated in the presence of IL-4, IL-6, and IL-21 and were transcriptionally unique from cells cultured with either IL-4 or the IL-6/IL-21 combination alone. In vivo, both STAT3 and STAT6 were required for GrA+ Th cell differentiation and played roles in maintenance of the lineage identity. Importantly, GrA+ Th cells promoted aGVHD-associated morbidity and mortality and contributed to crypt destruction within intestines but were not required for the beneficial graft-versus-leukemia effect. Our data indicate that GrA+ Th cells represent a distinct Th subset and are critical mediators of aGVHD.

An approach to predicting hematopoietic stem cell transplantation outcome using HLA-mismatch information mapped on protein structure data

In hematopoietic stem cell transplantation (HSCT), the outcome is predicted using HLA-matching procedures, which are very time-consuming. There exists substantial evidence of the importance of early donor acceptance in HSCT outcome. In cases when the donor cannot be perfectly matched, it often is unclear which mismatch is less harmful and thus has a greater likelihood of acceptance. We modeled and analyzed interactions between the protein products of different HLA alleles of the transplant recipient and natural killer and T lymphocyte cell receptors of the donor's immune system. Reactions between these 2 systems often lead to graft-versus-host disease (GVHD). Sequence polymorphisms that define HLA I and II alleles predict not only GVHD, but also host-versus-graft and graft-versus-leukemia effects, all of which influence the overall transplantation outcome. Although complete high-resolution HLA matching of the donor-recipient pair seems to be associated with optimal post-HSCT survival, recent reports suggest that not every HLA disparity is functionally relevant. We performed interaction energy calculations for selected pairs of donor-recipient HLA alleles. Based on the results, we conclude that the energy of contact between the T lymphocyte cell receptor (TCR) and HLA residues can help predict the future development of an immune reaction and, consequently, the outcome of allogeneic HSCT.

Granzymes A and B serum levels in allo-SCT

Activated cytotoxic T lymphocytes and natural killer cells, which are involved in the pathogenesis of GVHD and viral infections after SCT produce granzymes (Grs). This study performed an ELISA in the serum of 86 patients at various time points before and after Allo-SCT to investigate GrA and GrB levels as potential markers for these serious complications. The increase in Gr levels from the day of transplantation until the appearance of the complication was highly predictive. If GrA increased to three times its pretransplant level, the cumulative incidence of developing acute GVHD was 73% and for CMV infection 68%, in comparison with 45 and 35%, respectively, for patients without these complications. A strong increase in GrA level correlated with clinical severity of acute GVHD. No correlation was observed with early relapse or long-term overall survival. In addition to clinical parameters, a strong increase in GrA levels was identified as an independent marker for the occurrence of acute GVHD as well as for CMV infection. Similar effects were observed with GrB. In conclusion, Gr protein levels can also be used as a marker for complications after Allo-SCT.