Graft versus host disease (GVHD) represents the major complication after allogeneic hematopoietic stem cell transplantation (Allo-SCT). GVHD-prone patients rely on GVHD prophylaxis (e.g. methotrexate) and generalized anti-GVHD medical regimen (glucocorticoids). New anti-GVHD therapy strategies are being constantly explored, however there is an urgent need to improve current treatment, since GVHD-related mortality reaches 22% within 5 years in patients with chronic GVHD. This review is an attempt to describe a very well-known receptor in lipoprotein studies – the low-density lipoprotein receptor related protein 1 (LRP1) - in a new light, as a potential therapeutic target for GVHD prevention and treatment. Our preliminary studies demonstrated that LRP1 deletion in donor murine T cells results in significantly lower GVHD-related mortality in recipient mice with MHC (major histocompatibility complex) -mismatched HSCT. Given the importance of T cells in the development of GVHD, there is a significant gap in scientific literature regarding LRP1’s role in T cell biology. Furthermore, there is limited research interest and publications on this classical receptor molecule in other immune cell types. Herein, we endeavor to summarize existing knowledge about LRP1’s role in various immune cells to demonstrate the possibility of this receptor to serve as a novel target for anti-GVHD treatment.

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Adoptive transfer of leukemia specific CTL could prove to be a valuable tool in the prevention and/or treatment of relapse after SCT. In line with this, we chose to examine the use of PR1-specific CTL derived from UCB as a means of adoptive immunotherapy for leukemia. PR1, a 9 amino acid, HLA-A2-restricted self-peptide is well established as a dominant LAA. While cells specific for PR1 are present in the peripheral blood of healthy adults at extremely low frequencies (0.0005 to 0.05% of CD8+ T cells), we have found that the frequency of PR1-CTL in UCB is significantly higher ranging from 0.007 to 0.345% (mean 0.117%; n=57) of CD8+ cells. We hypothesized that these cells could be isolated directly from UCB via cell sorting and used in the prevention or treatment of leukemia. CD8 enriched cells were sorted and then activated ex vivo with anti-CD3/anti-CD28/IL-2. Sorted, activated cells were infused into a cohort of NSG mice with established leukemia. In three separate, but comparable, experiments the frequency of leukemia cells in the bone marrow of mice receiving PR1-specific CTL was reduced by 27% (range 21%-32%) compared to those receiving no treatment, and 23% (range 4%-47%) compared to those receiving non-specific CD8+ cells. The reduction of leukemia cells in the blood was even more pronounced with a 47% (range 45%-61%) decrease compared to the level seen in mice receiving PBS alone, and 58% (range 48%-68%) compared to mice receiving non-specific CD8+ cells.

Cytotoxic T lymphocytes (CTL) specific for PR1, a HLA-A*0201-restricted peptide derived from proteinase 3, are capable of killing leukemia cells and contribute to the elimination of CML. Cytogenetic remission of CML after treatment with IFNα correlates with an expansion of PR1-CTL in patients. INFα is also an abundant cytokine produced by plasmacytoid DC which is critical for priming adaptive immune responses and MHC class I antigen cross-presentation. To determine whether a clinical trial with adoptively transferred PR1-CTL will benefit leukemia patients, we used INFα in combination with GM-CSF for ex vivo expansion of PR1-CTL and examined whether theses PR1-CTL can eliminate AML in the established NOD/SCID model. PBMC from HLA-A*0201+health donors were stimulated weekly with autologous DC pulsed with PR1 peptide in the presence of INFα and GM-CSF. By 3 weeks, there were 38.7% of PR1-CTL in the culture compared to 1.83% detected in the original sample using PR1-tetramer staining. We found that PR1-CTL generated in vitro can migrate to sites of disease and maintain their capacity to eliminate the human primary AML cells in NOD/SCID mice. Mice received AML alone had 72–88% blasts in a hypercellular marrow, whereas mice that received AML plus PR1-CTL had normal hematopoietic elements and only 10–11% blasts in a hypocellular marrow. We conclude that ex vivo expansion of PR1-CTL using this method is suitable for adoptive immunotherapy of AML.

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