Flow chart of one method of engineering T cells to fight cancer.

Tough blood cancers are responding to treatment with the patient's own genetically engineered immune cells, according to a cancer specialist who is helping test the bold -- and risky -- approach.

The treatment has produced complete remissions in large percentages of patients treated, up to 90 percent in one group of 30 patients. Moreover, these are all extremely sick patients, whose cancer has resisted other therapies, leaving them with virtually no options. The longest survivor has been in complete remission for more than 4 years, said Dr. David Porter of the University of Pennsylvania.

Porter spoke Sunday at the 35th Annual Conference on Clinical Hematology & Oncology, held in La Jolla by Scripps Health. Speakers like Porter came from around the country to discuss advances in their field, part of a continuing medical education program to keep doctors up to date with the latest medical advances. The conference continues through Tuesday.

Dr. David Porter / University of Pennsylvania

Porter works with Dr. Carl June and other colleagues to hone the effectiveness of using T cells genetically programmed to attack malignant B cells. B cell malignancies cause such cancers as chronic lymphocytic leukemia, or CLL; acute lymphoblastic leukemia, or ALL, and non-Hodgkin's lymphoma.

The genetically altered T cells are given an artificially created gene to produce a chimeric antigen receptor. This receptor recognizes the protein CD19, produced almost exclusively on B cells. The T cells hone in on this protein and kill the B cells. When the cancer is knocked down, some of the T cells remain behind, ready to pounce on any recurrence.

The trials are now expanding to include myloma, Porter said. For more information on the university's T cell-based clinical trials, go to http://www.penncancer.org/tcelltherapy.

June's team began testing the therapy in 2010 in CLL patients and then in those with ALL. These were all patients with relapsed cancers that had become resistant to other therapies. The therapy has been progressively refined, Porter said. Other centers have developed their own versions of this therapy.

In October, 2014, the University of Pennsylvania and Children's Hospital of Philadelphia announced that 27 out of 30 patients with relapsed ALL achieved a complete remission within one month of treatment, and 23 were still alive 6 months after treatment. As of October, 19 of the patients remained in remission. Most treated, 25 out of 30, were children. The response rate with CLL is about 47 percent, Porter said.

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Cancer gene therapy advances

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