Granulocyte colony stimulating factor (G-CSF), granulocyte macrophage colony stimulating factor (GM-CSF) and macrophage colony stimulating factor (M-CSF) are cytokines that stimulate the bone marrow to produce blood cells. G-CSF and GM-CSF are licensed drugs for the treatment of white blood cell shortages (neutropenia) in some medical conditions.

G-CSF is also known as lenograstim or filgrastim, or by its trade name Neupogen. GM-CSF is sometimes referred to by the generic name molgramostim and is produced by Sandoz and Schering-Plough under the trade name Leucomax. Another GM-CSF is known as sargramostim, with the brand name Leukine. Sargramostim is being developed by Immunex Corporation.

GM-CSF has been shown to be safe and effective in improving white cell counts in people with neutropenia due to AZT (zidovudine, Retrovir) treatment^[1][2]. Several randomised controlled studies have also demonstrated that GM-CSF has anti-HIV effects, since it can reduce the incidence of infections and death, and enhance CD4 cell count increases and viral load suppression when added to antiretroviral therapy^[3][4]. Among HIV-positive people with low white blood cell counts, G-CSF has also been shown to prevent severe neutropenia and illness, as well as increasing CD4 and CD8 cell counts in when added to stable antiretroviral therapy^[5].

It is not clear how colony stimulating factors work. Current theories include altering the expression of HIV receptors on white blood cells, interfering with HIV replication or stimulating the production of cytokines^[6][7].

Despite these findings, not all studies have found beneficial effects in patients with HIV. They are also very expensive, and can only be given by injection.

Colony stimulating factors commonly cause side-effects, including bone or muscle pain, difficulty or pain when urinating, liver abnormalities, lethargy, skin rashes and inflammation of the blood vessels. Some people also experience unpleasant side-effects after the first injection, including flushing, low blood pressure, rapid heartbeat, breathlessness, nausea and vomiting.