Mammalian immune system guards the host against invading pathogens. Deficient immune system makes the host susceptible to many opportunistic infections. Immunodeficiency could be primary, caused by genetic or developmental defect or secondary caused by drugs, ionizing radiation. The deficient immune system caused due to natural causes or deliberate medical intervention, could be rectified or replenished by the adult stem cells, called haematopoietic stem cells derived from various sources. The aim of the review is to summarize our current knowledge about the haematopoietic stem cell transplantation in the modulation of the altered or damaged immune system. Further the scope of innovative stem cell therapy is considered in treating other diseases.
