Depletion of recipient NK cells significantly increases engraftment of haplo-matched highly purified hematopoietic stem cells

Abstract

Hematopoietic stem cell transplantation has been shown to be a potential curative treatment for malignant and nonmalignant hematopoietic disorders. However, many patients lack an HLA identical matched donor, and haplo-matched transplanted patients are at risk of developing acute and chronic graft versus host disease (GvHD). Preparations of purified hematopoietic stem cells (HSC) depleted of T cells greatly decrease the risk of GvHD. However, transplantation of allogeneic haplo or completely mismatched purified HSC results in greater resistance to engraftment compared to whole bone marrow. An earlier study demonstrated that barriers to engraftment of allogeneic HSC may be decreased by increasing the stem cell dose (Uchida et al., 1998); however, the mechanism of inhibition of engraftment of purified HSC was not shown. Our study evaluated hematopoietic recovery kinetics (WBC, RBC, and platelets) and long-term functional immune restoration of highly purified mouse KTLS HSC in syngeneic, MHC-matched unrelated (MUD) and haplo-identical transplantation models. Mice transplanted with haplo-identical HSC exhibited slower recovery kinetics, decreased levels of donor chimerism and survival at all HSC doses tested as compared to syngeneic or MUD HSC. Pretreatment of recipients with antibody to clear residual NK cells improved recovery kinetics, donor chimerism and survival of haplo-identical HSC transplants equal to levels observed with syngeneic HSC transplants. Analysis of transplanted mice revealed no quantitative differences of donor B and T lymphoid, myeloid, or NK cells in the bone marrow, spleen, thymus, lymph nodes and peripheral blood. Progenitor compartments and B and T lymphoid maturation pathways appeared normal. Immunization of haplo-identical HSC transplanted mice with ova, elicited a specific T-mediated B cell response in all three transplant models. These data illustrate that depletion of residual host NK cell activity in preparation for purified haplo-identical HSC transplantation results in rapid early immune recovery and a quantitative and qualitative restoration of the adaptive immune response equivalent to fully matched HSC. Our studies suggest the potential clinical use of purified haplo-identical HSC could be safely broadened by depletion of host NK cells in transplant patients without a matched related donor.