Combinatorial suicide gene strategies for the safety of cell therapies.

Gene-modified cellular therapies carry inherent risks of severe and potentially fatal adverse events, including the expansion of alloreactive cells or malignant transformation due to insertional mutagenesis. Strategies to mitigate uncontrolled proliferation of gene-modified cells include co-transfection of a suicide gene, such as the inducible caspase 9 safety switch (ΔiC9). However, the activation of the ΔiC9 fails to completely eliminate all gene-modified cells. Therefore, we tested a two suicide gene system used independently or together, with the goal of complete cell elimination. The first approach combined the ΔiC9 with an inducible caspase 8, ΔiC8, which lacks the endogenous prodomain. The rationale was to use a second caspase with an alternative and complementary mechanism of action. Jurkat cells co-transduced to co-express the ΔiC8, activatable by a BB homodimerizer, and the ΔiC9 activatable by the rapamycin analog sirolimus were used in a model to estimate the degree of inducible cell elimination. We found that both agents could activate each caspase independently, with enhanced elimination with superior reduction in cell regrowth of gene-modified cells when both systems were activated simultaneously. A second approach was employed in parallel, combining the ΔiC9 with the RQR8 compact suicide gene. RQR8 incorporates a CD20 mimotope, targeted by the anti-CD20 monoclonal antibody rituxan, and the QBend10, a ΔCD34 selectable marker. Likewise, enhanced cell elimination with superior reduction in cell regrowth was observed when both systems were activated together. A dose-titration effect was also noted utilizing the BB homodimerizer, whereas sirolimus remained very potent at minimal concentrations. Further in vivo studies are needed to validate these novel combination systems, which may play a role in future cancer therapies or regenerative medicine.

Plasma cell leukaemia with t(11;14) not responsive to venetoclax.

A 70-year-old man with medical history of IgG kappa multiple myeloma, initially diagnosed in 2017, underwent induction therapy with carfilzomib, lenalidomide and dexamethasone followed by autologous haematopoietic stem cell transplantation. Nine months following transplant, disease relapsed in the form of plasma cell leukaemia. Fluorescent in situ hybridisation of malignant plasma cells revealed t(11;14). A combination therapy including venetoclax was used based on efficacy data for Bcl-2 inhibitor venetoclax from available early-phase clinical trials in patients with relapsed multiple myeloma with t(11;14) and other published case studies. Unfortunately, the disease was primary refractory, and after further ineffective therapies, the patient did not have a successful outcome.

Colon metastases as first clinical manifestation of lobular breast carcinoma with no subsequent evidence of breast disease.

A 73-year-old woman was brought to the oestrogen receptor for altered mental status. She was found to be hypotensive and hypoglycaemic and admitted to the intensive care unit. She had a history of chronic watery diarrhoea which had recently increased over the last 2 weeks and was associated with vague abdominal pain. A CT showed bowel wall thickening concerning for colitis. Due to the increasing diarrhoea, a colonoscopy was done after all stool studies came back negative. Polyps in the ascending, transverse and sigmoid colon were found to be tubular adenomas but random colonic mucosa biopsies were revealed to be histologically consistent with metastatic lobular breast carcinoma. Further workup revealed no primary breast disease.