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[18F]-Fhbg-PET/CT Imaging of CD34-TK75+ T Cells in Allogeneic HSCT Recipients after Donor Lymphocyte Infusion (IND#11917; Clinicaltrials.Gov Identifier: NCT00871702)
Background: Allogeneic transplantation is associated with both GvL and GvHD. Elimination of donor T cells results in less GvHD, but also less GvL and engraftment. To eradicate infused T cells if GvHD develops, our suicide gene based therapy uses a CD34-Herpes Simplex Virus-1-thymidine kinase (CD34-TK75) chimera (Rettig et al, Mol Ther 2003 and J Immunol 2006). We enrich and purify retrovirally transduced cells via cell surface expression of the extracellular domain of CD34. Modified TK75 both mediates cell suicide upon treatment with ganciclovir and enables tracking of modified cells that entrap the substrate, [18F]FHBG (9-[4-fluoro-3-hydroxymethyl-butyl]guanine) by PET/CT. Methods: Following production and release testing of CD34-TK75 transduced and affinity-purified T cells (88-98.8% CD34+), we began a phase I pilot and feasibility study. Cells were infused as a DLI (0.1-1.3 x 106 CD34-TK75+ T cells/kg) into 8 patients (relapsed after allo-HSCT). Since no toxicities were observed during treatment of our first 2 patients, we initiated trafficking studies using [18F]-FHBG-PET/CT imaging at baseline, d15, and d30 after infusion of CD34TK75+ T cells in patients 3-8. Results: No acute toxicities were associated with administering either genetically modified T cells or [18F]FHBG. Using real-time quantitative PCR, we detected the CD34-TK75 transgene in the circulating CD34-TK75+ T cells of all but one patient. GvHD developed in only one patient (grade III GI) who did not respond to a 10 day treatment with I.V. ganciclovir (10 mg/kg). CD34-TK75 transgene could not be detected in the peripheral blood of this patient at the time of GvHD. Patient samples were also tested for replication competent retrovirus and for integration sites both by Ligation Mediated-PCR and hybrid capture. Baseline levels of [18F]FHBG were low, primarily characterized by renal excretion, which should permit detection of T cell expansion in the lymphoid organs or intestines. However, pharmacokinetics of the radiolabel were similar in the one patient that did and those that did not develop GvHD (Fig. 1). In parallel experiments, NOD/SCIDg mice were injected (i.o.) with 2 x 106 CD34-TK75+ T cells (patients 2-8; n=2 mice per donor). Control mice received conditioning only. Using micro-PET/CT with [18F]FHBG, we detected CD34-TK75+ human T cells in the thymus and lymph nodes only in mice that developed GvHD. Summary: This "first-in-man" study demonstrated the safety and feasibility of manufacturing both CD34-TK75+ T cells and [18F]FHBG onsite for administration to patients. A future upfront haploidentical transplant study will employ 100-fold more CD34-TK75 modified T cells.
SHAPE \* MERGEFORMAT
| Baseline scan |
| 14-Day scan |
| 30-Day scan |
| TK04 (no GvHD) |
| ANT |
| ANT |
| ANT |
| POST |
| POST |
| POST |
| Baseline scan |
| 14-Day scan |
| 30-Day scan |
| TK07 (Liver GvHD) |
| ANT |
| ANT |
| ANT |
| POST |
| POST |
| POST |