The study will collect up to 18 patients with multiple myeloma, melanoma and/or two types of sarcoma. Penn scientists will use CRISPR to delete two particular genes in patients' T cells: The first, PD-1, can be manipulated by cancer cells to impede the immune system, while the second is an alarm-sounding receptor that will be removed and replaced with one engineered to alert the body to specific tumors.

The Penn scientists won't be injecting CRISPR directly into patients' bloodstreams; Instead, they'll use a method called ex vivo gene therapy, extracting blood and editing it with CRISPR before re-inserting it into subjects. This may bypass certain immune reactions that reject the former method. Last week, scientists published a study that found between 65 and 79 percent of human subjects produced antibodies fighting proteins made by two variants of the CRISPR Cas9 technique.

Penn scientists haven't announced a start date for their record-setting CRISPR study: "We are in the final steps of preparing for the trial, but cannot provide a specific projected start date," a Penn Medicine spokesperson told MIT Technology Review.