Cancer Immune Therapy Edited by G. Stuhler and P. Walden ...

306 15 Bone Marrow Transplantation for Immune Therapy
procedure was observed. These data confirm the therapeutic potential and safety of
HSV-tk-modified T cells in the context of allografting. The immunologic in vivo potential
of transduced lymphocytes is maintained in terms of immune reconstitution
early after transplantation, antitumor effect and alloreactivity. GCV in vivo administration
has been confirmed as a specific method for the elimination of HSV-tk cells
and modulation of DLI effects.
15.8
HSV-tk Lymphocyte Add-backs after Haploidentical Transplantation
The program of reinfusion of tk-engineered donor lymphocytes has been extended
to haploidentical transplantation for hematological malignancies. Haploidentical
transplantation remains the only option available for a number of individuals who
lack a HLA-compatible family or unrelated donor [32]. However, there is a reluctance
to undertake such a procedure due to the high rates of morbidity and mortality. The
depletion of T cells from the initial graft results in an increased frequency of infective
complications and allows disease relapse or progression. A strategy whereby donor
T cells are added back in an incremental fashion at specific time points after
haplo-cell transplantation may permit enhanced immune recovery with protection
from infection and prevent relapse of malignancy, but obviously runs the risk of
severe GvHD. The incorporation of a suicide gene into these cells would provide the
ability to control GvHD should this complication arise. We recently designed a clinical
protocol for programmed tk-DLI for immune reconstitution and relapse prevention
after haplo-stem cell transplantation (SCT). Seven patients with high-risk hematologic
malignancies who underwent haplo-SCT (four chemorefractory AML, one
CR2 ALL, one multiple myeloma and one CR2 AML) received escalating doses of tk-
DLI starting from 42 days after SCT (dose escalation: 5 × 10 4 ±10 7 /kg). At the time of
infusion, no circulating CD3 + cells could be detected. Infused lymphocytes were
100% CD3 + and 13±50% CD4 + . Circulating tk-transduced cells were documented in
six of seven patients (peak 2±63 cells/ml, median day of engraftment +28, range +12±
43). Two of seven patients reached 50 CD3 + /ml by day 30, increasing steadily thereafter.
Functional analysis of ex vivo PBLs showed that engrafted T cells were fully
functional, being able to proliferate and produce high levels of interferon-g after
polyclonal stimulation. Moreover, when immune reconstitution was achieved, T cells
specific for allogeneic and viral antigens could be demonstrated ex vivo. One out of
four of the chemorefractory AML patients maintained CR for over 3 months after
the infusion, while the other three patients relapsed during the first month after tk-
DLI before tk cells engraftment. Two of two chemorefractory AL and one of one multiple
myeloma maintained CR for over 6 months after tk-DLI. No acute GvHD was
observed in this initial series of patients. In those patients who achieved immune reconstitution
after tk-DLI, no additional anti-CMV treatment was required. However,
four of seven patients had to be treated with GCV within the first 30 days after infusion,
before immune reconstitution was achieved, to control CMV infection resistant
to foscarnet. This resulted in the rapid in vivo elimination of tk cells. Three patients