The CD68 protein as a potential target for leukaemia-reactive CTL

Abstract

CD68, a haematopoietic differentiation marker of the monocyte-macrophage lineage, is expressed in various human malignancies including chronic and acute myeloid leukaemia (AML). While the majority of normal CD34 + cells are negative for CD68 expression, CD34 + cells from AML patients produce elevated amounts of this protein. The purpose of this study was to identify CTL epitopes in the human CD68 protein. Mouse CD68 was also analysed to search for epitopes that could be used in murine tumor model. Peptides binding to murine H2 b class I molecules were identified and used to stimulate CTL responses from allogeneic donor mice to avoid immunological tolerance. High avidity CTL clones specific for three different peptide epitopes did not kill CD68-expressing murine target cells, indicating that endogenous antigen processing failed to produce sufficient amounts of these peptides. In contrast, allorestricted human CTL specific for an HLA-A2-binding peptide of CD68 recognised not only picomolar concentrations of peptide, but also displayed low levels of killing against HLA-A2-positive K562 and THP-1 leukemia cell lines and blast cells from AML patients. These data suggest that human leukaemia cells express limited amounts of CD68-derived peptides, and that high avidity CTL capable of recognising sub-picomolar concentrations of peptides are required for efficient killing of leukaemia cells. Leukemia (2002) IntroductionThe success of tumour immunotherapy is largely dependent on the choice of target antigen. Tumour-associated antigens, that are targeted by various immunotherapy strategies fall into three categories: viral antigens, products of mutated genes and normal cellular proteins. The latter category, which comprises differentiation antigens, has been extensively exploited for the treatment of solid tumours, such as melanoma and prostate cancer. 1 Self-tolerance to differentiation antigens expressed in non-haematopoietic cells is probably not absolute, providing an explanation for the detection of CTL against these antigens in tumour patients. The use of haemopoietic differentiation antigens, however attractive it may appear for the purposes of targeting cellular immune responses against leukaemic blast cells, is limited by potent tolerogenic effects of haemopoietic cells. Hence, it is likely that autologous T cells specific for haemopoietic differentiation antigens have been deleted in the thymus or rendered unresponsive by peripheral tolerance mechanisms.In the past few years, we have developed a strategy to circumvent tolerance to self proteins. 2 The allo-restricted strategy is based on the observation that T cell tolerance is self-MHC restricted. Hence, T cells from A2-negative donor individuals can mount CTL responses against epitopes from self-proteins presented by A2 class I molecules. Using this strategy, we have previously identified CTL epitopes in the self-proteins mdm2 and cyclin D1, and shown that the CTL selectively killed tumour cells expressing large quantities of these proteins but not normal ce...

Efficient Lung Recruitment of Respiratory Syncytial Virus-Specific Th1 Cells Induced by Recombinant Bacillus Calmette-Guérin Promotes Virus Clearance and Protects from Infection

“…A stop solution was added, and the absorbance of the sample was measured at 490 nm. The amount of cell-mediated cytotoxicity was calculated by subtracting the spontaneous LDH released from the target and effector cells from the LDH released by lysed target cells, as indicated by the manufacturer (28,29) …”

Immunotherapy of Acute Myeloid Leukemia: Current Approaches

“…In addition to the antigens described above, it was established, in vitro, that CTLs with the potential to kill leukemic cells also could be generated against other LAAs, such as CD68, human neutrophil elastase, and proteinase 3 [35]. In conclusion, following promising in vitro data using different antigens, clinical trial data are needed to further evaluate the safety and efficacy of this passive AML immunotherapy strategy [35][36][37].…”

“…In conclusion, following promising in vitro data using different antigens, clinical trial data are needed to further evaluate the safety and efficacy of this passive AML immunotherapy strategy [35][36][37].…”

Antigen-specific cellular immunotherapy of leukemia

“…55,64 Using this method, high-avidity CTL could be established from HLA-A2-negative donors recognizing HLA-A2-presented epitopes from overexpressed leukemia-associated proteins, such as WT1, CD45 and CD68. 24,55,[65][66][67][68][69] At present, established human WT1-specific CTL clones, such as TAK-1, 70 NIM-1 62 and 77, 24 have been found to induce lysis of endogenously WT1-expressing tumor cells in vitro, to inhibit in vitro colony formation by leukemic CD34 þ cells and to impair engraftment of human leukemic cells in immunodeficient NOD-SCID mice. Importantly, WT1-specific CTL did not cause damage to physiologically WT1-expressing normal cells or impair normal hematopoiesis, 71 notwithstanding the fact that WT1 expression levels in a proportion of normal CD34 þ hematopoietic progenitor and stem cells were comparable to those observed in leukemic cells.…”