A German man remains in remission from HIV an incredible six years after he received a stem cell transplant to treat an aggressive form of leukemia. The seventh known HIV patient to achieve long-term remission, the patient known as Berlin 2 (B2), received donor stem cells containing only one copy of a mutated gene known to confer resistance to HIV, unlike the two copies present in donor cells given to other patients. The single-copy cells were thought to provide a short-lived but less durable