The present report describes work examining the manner in which nonmalignant bone marrow stromal cells prevent acute lymphoblastic leukemia (ALL) cell death. The initial focus was on the role of stromal cell-derived C-X-C motif chemokine 12 (CXCL12). Interference with CXCL12 production by stroma or blockade of its interactions with ALL by plerixafor did increase ALL cell death and in sensitive ALLs there was synergistic effect with conventional chemotherapy drugs. However, in contrast to most reports, there was considerable heterogeneity regarding the effect between 7 unique primary ALLs, with several exhibiting no sensitivity to CXCL12 blockade. The diversity in effect was not explained by differences in the expression of ALL cell surface receptors for CXCL12. The modest and variable effects of interference with CXCL12 on ALL led to the assessment of gene expression profiles of stromal cells and ALL cells. Gene set enrichment analysis identified pathways associated with metabolism and redox reactions as potentially important in the stromal cell: leukemia cell interaction. Exploratory imaging studies demonstrated bidirectional transfer of intracellular calcien-labelled molecules and also bidirectional transfer of mitochondria between stromal cells and ALL cells, providing potential means of metabolic interdependence of stromal cells and ALL cells.

The clinical success of allogeneic T-cell therapy for cancer relies on the selection of antigens that can effectively elicit antitumor responses with minimal toxicity toward nonmalignant tissues. While minor histocompatibility antigens (MiHA) represent promising targets, broad expression of these antigens has been associated with poor responses and T-cell dysfunction that may not be prevented by targeting MiHA with limited expression. In this study, we hypothesized that antitumor activity of MiHA-specific CD8 T cells after allogeneic bone marrow transplant (BMT) is determined by the distribution of antigen relative to the site of tumor growth. To test this hypothesis, we utilized the clinically relevant male-specific antigen HY and studied the fate of adoptively transferred, HY-CD8+ T cells (HY-CD8) against a HY-expressing epithelial tumor (MB49) and pre-B cell leukemia (HY-E2APBX ALL) in BMT recipients. Transplants were designed to produce broad HY expression in nonhematopoietic tissues (female → male BMT, [F>M]), restricted HY expression in hematopoietic tissues (male → female BMT, [M>F]) tissues, and no HY tissue expression (female → female BMT, [F>F]). Broad HY expression induced poor responses to MB49 despite sublethal GVHD and accumulation of HY-CD8 in secondary lymphoid tissues. Antileukemia responses, however, were preserved. In contrast, restriction of HY expression to hematopoietic tissues restored MB49 responses but resulted in a loss of antileukemia responses. We concluded that target alloantigen expression in the same compartment of tumor growth impairs CD8 responses to both solid and hematologic tumors.

The effectiveness of allogeneic graft-versus-leukemia (GVL) activity in control of acute lymphoblastic leukemia is generally regarded as poor. One possible factor is dynamic adaptation of the leukemia cell to the allogeneic environment. This work tested the hypothesis that the pattern of gene expression in acute lymphoblastic leukemia cells in an allogeneic environment would differ from that in a non-allogeneic environment. Expression microarray studies were performed in murine B lineage acute lymphoblastic leukemia cells recovered from mice that had undergone allogeneic MHC-matched but minor histocompatibility antigen mismatched transplants. A limited number of genes were found to be differentially expressed in ALL cells surviving in the allogeneic environment. Functional analysis demonstrated that genes related to immune processes, antigen presentation, ubiquitination and GTPase function were significantly enriched. Several genes with known immune activities potentially relevant to leukemia survival (Ly6a/Sca-1, TRAIL and H2-T23) were examined in independent validation experiments. Increased expression in vivo in allogeneic hosts was observed, and could be mimicked in vitro with soluble supernatants of mixed lymphocyte reactions or interferon-gamma. The changes in gene expression were reversible when the leukemia cells were removed from the allogeneic environment. These findings suggest that acute lymphoblastic leukemia cells respond to cytokines present after allogeneic transplantation and that these changes may reduce the effectiveness of GVL activity.