Antiviral responses following L-leucyl-L-leucine methyl esther (LLME)-treated lymphocyte infusions: graft-versus-infection without graft-versus-host disease.

Although allogeneic hematopoietic progenitor cell transplant (HPCT) is curative therapy for many disorders, it is associated with significant morbidity and mortality, which can be related to graft-versus-host disease (GVHD) and the immunosuppressive measures required for its prevention and/or treatment. Whether the immunosuppression is pharmacologic or secondary to graft manipulation, the graft recipient is left at increased risk of the threatening opportunistic infection. Refractory viral diseases in the immunocompromised host have been treated by infusion of virus-specific lymphotyces and by unmanipulated donor lymphocyte infusion (DLI) therapy. L-leucyl-L-leucine methyl ester (LLME) is a compound that induces programmed cell death of natural killer (NK) cells, monocytes, granulocytes, most CD8(+) T cells, and a small fraction of CD4(+) T cells. We have undertaken a study of the use of LLME-treated DLI following T cell-depleted allogeneic HPCT, specifically to aid with immune reconstitution. In this ongoing clinical trial, we have demonstrated the rapid emergence of virus-specific responses following LLME DLI with minimal associated GVHD. This paper examines the pace of immune recovery and the rapid development of antiviral responses in 6 patients who developed viral infections during the time period immediately preceding or coincident with the administration of the LLME DLI.

Heterogeneous clearance of antithymocyte globulin after CD34+-selected allogeneic hematopoietic progenitor cell transplantation.

Antithymocyte globulins (ATG) are purified, concentrated preparations of polyclonal immunoglobulin G from hyperimmune serum of horses or rabbits immunized with human thymus lymphocytes. Both the horse and the rabbit products induce immunosuppression as a result of lymphocyte depletion and immune modulation. The exact mechanism of action is unknown but may include T-cell clearance from the circulation and modulation of T-cell activation, homing, and cytotoxic activities. Both horse and rabbit ATG include multiple antibodies against T-cell surface antigens and have been used extensively in allogeneic hematopoietic progenitor cell transplantation (HPCT) for the treatment and prevention of graft-versus-host disease or graft rejection. To quantify the active ATG after HPCT, we developed a flow-based assay to measure residual ATG capable of binding to lymphocytes. In contrast to prior assays that measure total rabbit or horse immunoglobulin, this assay quantitates only the antibody capable of binding to lymphocytes, which presumably reflects the functionally active fraction of the xenoantiserum. Thirty patients with hematologic malignancies underwent T cell-depleted HPCT and had ATG levels assayed during the peritransplantation period. The time required for ATG levels to decay to background was quite variable (mean, 46 days; range, 14-91 days), although most patients demonstrated a rapid early clearance followed by a slower decline. The actual mean half-life was 6.8 days (range, 2.4-14.0 days). The persistence of ATG for months after administration has significant implications for the pace of immune reconstitution after transplantation and is a potentially confounding variable in any study that involves early administration of donor lymphocyte infusions or other cellular transfer. These findings indicate that ATG levels should be explicitly measured in studies that involve early donor lymphocyte administration so that proper conclusions regarding dose, safety, and efficacy can be reached.

A randomized, placebo-controlled trial of subcutaneous administration of GM-CSF as a vaccine adjuvant: effect on cellular and humoral immune responses.

Thirty healthy volunteers were randomly assigned to receive either a single subcutaneous injection of GM-CSF or placebo at the time of vaccination with tetanus and diptheria toxoid (Td), influenza and hepatitis A vaccines. Humoral response was measured by weekly serum samples assayed for antibodies to tetanus toxoid (TT), influenza and hepatitis A; while cellular response to TT was determined by measuring IL-2 expression in T-cells following in vitro exposure to TT antigen using a flow cytometric assay. It was hypothesized that (1). GM-CSF would augment immune response and (2). that the frequencies of TT responsive T-cells in the blood would predict humoral responses. The administration of subcutaneous GM-CSF as an adjuvant at the time of vaccination did not augment the antibody responses to influenza or hepatitis A in normal volunteers when compared to placebo. Subjects who received GM-CSF had statistically significant lower increases in anti-tetanus antibodies than placebo recipients. Immunization with TT resulted in an increase in the frequency of antigen responsive T-cells in the blood over time. The frequencies of TT responsive T-cells in baseline blood samples were correlated with baseline anti-tetanus antibody titers, but humoral and cellular responses were not correlated following vaccination. Recipients of GM-CSF did not develop significantly higher numbers of TT responsive T-cells after vaccination compared to recipients who received placebo.