Donor and host photoreceptors engage in material transfer following transplantation of post-mitotic photoreceptor precursors.

Photoreceptor replacement by transplantation is proposed as a treatment for blindness. Transplantation of healthy photoreceptor precursor cells into diseased murine eyes leads to the presence of functional photoreceptors within host retinae that express an array of donor-specific proteins. The resulting improvement in visual function was understood to be due to donor cells integrating within host retinae. Here, however, we show that while integration occurs the majority of donor-reporter-labelled cells in the host arises as a result of material transfer between donor and host photoreceptors. Material transfer does not involve permanent donor-host nuclear or cell-cell fusion, or the uptake of free protein or nucleic acid from the extracellular environment. Instead, RNA and/or protein are exchanged between donor and host cells in vivo. These data require a re-evaluation of the mechanisms underlying rescue by photoreceptor transplantation and raise the possibility of material transfer as a strategy for the treatment of retinal disorders.

A phase II study evaluating the toxicity and efficacy of single-agent temsirolimus in chemotherapy-naïve castration-resistant prostate cancer.

BACKGROUND: The mammalian target of rapamycin (mTOR) pathway is deregulated in castration-resistant prostate cancer (CRPC). We investigated the efficacy and toxicity of temsirolimus, an mTOR inhibitor, in chemotherapy-naïve CRPC. METHODS: In this phase II open label study, eligible patients received IV temsirolimus at 25 mg weekly until objective disease progression, unacceptable toxicity or investigator's discretion. Toxicity was assessed every 4 weeks and responses every 8 weeks. Primary end point was calculating the overall response (OR) rate as well as measuring stable disease (SD) to assess the overall clinical benefit calculated as OR+SD. Secondary end points included prostatic-specific antigen (PSA) changes and time to progression biochemically and radiographically. Correlative studies included prospective assessment of quality of life (QoL) using two previously validated scales. RESULTS: Although the sponsor halted the study early, 21 patients were enrolled of which, 15 were evaluable for efficacy and OR. Median age was 74 (range: 57-89), median PSA was 237.5 ng ml(-1) (range: 8.2-2360), visceral disease present in 11 patients (52%), and 17 patients (81%) patients had Gleason score (7-10). Two patients had a partial response (PR) and eight had SD. The OR was 13% (2/15) and the overall clinical benefit (OR+SD) was 67% (10/15). Median time to radiographic disease progression was 2 months (range 2-10 months). Biochemical response assessment was available for 14/15 patients. Any PSA decline was observed in four patients (28.5%; 4/14) with one patient (7%) having >50% PSA decline. Median time to progression by PSA was 2 months (range 1-10 months). With a median follow-up of 32 months, median overall survival (OS) was 13 months (range: 2-37) and three patients remain alive at the data cutoff (5/2013) for an OS of 14% at 4 years on an intent-to-treat analysis. Major non-haematologic toxicities included fatigue (19%) and pneumonia (14%). Main laboratory toxicities included hyperglycaemia (24%) and hypophosphatemia (14%). Also, 52% of enrolled patients had serious adverse events. Other toxicities were consistent with previously reported adverse events with temsirolimus. Despite these observed adverse events, temsirolimus did not adversely impact QoL. CONCLUSION: Temsirolimus monotherapy has minimal activity in chemotherapy-naïve CRPC.