* Ribozyme Pharmaceuticals Inc., of Boulder, Colo., Chiron Corp., of Emeryville, Calif., City of Hope National Medical Center, of Duarte, Calif., and Children's Hospital, in Los Angeles, began a Phase I/IIa clinical study of a gene therapy to treat AIDS. The treatment involves inserting ribozymes into stem cells that replenish immune system cells. The ribozymes are designed to protect cells against HIV infection.

* Schering-Plough Corp., of Madison, N.J., entered an agreement with American Home Products Corp., of Madison, N.J., under which Schering-Plough will transfer all rights to interleukin-11 (IL-11) to American Home Products for an undisclosed cash amount. Schering-Plough said it will focus development efforts on interleukin-4 and interleukin-10, both Schering-Plough products in clinical testing. Schering-Plough licensed IL-11 from Genetics Institute Inc., of Cambridge, Mass., prior to its takeover by American Home Products. The drug is under review by the FDA for restoring platelets depleted by cancer chemotherapy.

* Sepracor Inc., of Marlborough, Mass., has completed a 362-patient Phase III bronchodilation study that demonstrated an improved therapeutic index for levalbuterol compared with racemic albuterol. Sepracor is developing single isomer versions of FDA-approved drugs to reduce side effects. The company expects to file a new drug application for levalbuterol by June 30, 1997.

* Sheffield Medical Technologies Inc., of New York, said it signed a letter of intent to acquire privately held Camelot Pharmacal LLC, of St. Louis, Mo. Financial terms were not disclosed. The acquisition is expected to be complete by the end of May 1997.

* Verigen Inc., of Guilford, Conn., said it began marketing its autologous chondrocyte implants in Denmark, Sweden and Norway through a subsidiary, Verigen Transplantation Services ApS, in Copenhagen, Denmark. The implants are used to treat cartilage defects in knees. Chondrocytes from a patient's healthy cartilage are multiplied in a laboratory and re-implanted to repair the damaged joint.

* Watson Pharmaceuticals Inc., of Corona, Calif., reports its wholly owned subsidiary, Oclassen Pharmaceuticals Inc., of San Rafael, Calif., has received approval from the FDA to market Condylox Gel for the treatment of external genital and perianal warts. The product is expected to be launched in the second quarter of fiscal 1997.