Engineering hematopoietic grafts: Purified allogeneic hematopoietic stem cells plus expanded CD8(+) NK-T cells in the treatment of lymphoma

A major benefit of allogeneic hematopoietic cell transplantation (HCT) in t he treatment of malignancies is the graft-versus-tumor (GVT) effect conferr ed by lymphocytes contained within the graft. However, lymphocytes can also induce the potentially lethal complication of graft-versus-host disease (G VHD). We have previously reported a method of generating large numbers of e x vivo activated and expanded T cells with antitumor activity after culture with interferon-gamma, cross-linking antibodies to CD3, and interleukin-2. Murine splenocytes expanded under these conditions are a heterogeneous pop ulation of which approximately 20% to 60% of cells express natural killer ( NK)-cell markers (NK1.1 and DX5) and display major histocompatibility compl ex (MHC)-unrestricted antitumor activity. Here we demonstrate the in vivo a ntitumor activity of this population of expanded CD8(+) NK-T cells when tra nsplanted across MHC barriers into tumor-beating hosts. In cotransfer studi es with purified allogeneic hematopoietic stem cells, expanded CD8(+) NK-T cells confer GVT activity with minimal to no GVHD. In vitro studies show th at, although expanded NK-T cells lyse normal allogeneic bone marrow cells, they preferentially mediate cytolysis against tumor targets. These cells pe rsist in the peripheral circulation of host animals for at least 3 weeks po sttransfer. GVT activity is dependent on perforin, but not on Fas-ligand. W e conclude that expanded CD8(+) NK-T cells may serve as a valuable adjuvant population for allogeneic HCT because they mediate GVT effects with minima l GVHD.