The human body has many lines of defense against infection, keeping us healthy and free of disease. One immediate line of defense is the innate immune system, which is comprised of white blood cells that are ready to fight against bacterial of fungal infection at birth. One of the most numerous and important cells of the innate immune system is phagocytic granulocytes or neutrophils. These cells spend most of their lives circulating in the peripheral blood, but once stimulated by a sequence of inflammatory events these cells migrate to areas of infection or injury and engulf bacteria, other microorganisms, and microscopic particles.
The body has checks and balances in place to prevent fluctuations in neutrophil numbers, but during times of infection, acute inflammation, or stress neutrophil numbers increase to fight the issue at hand. However, a decline in neutrophil number, known as neutropenia, can have detrimental effects. Neutropenia is problematic for patients recovering from chemotherapy treatment or hematopoietic stem cell transplantation. Frequent and prolonged periods of neutropenia lead to opportunistic bacterial or fungal infection. Current treatment for chemotherapy-induced neutropenia include stimulating white blood cell production by granulocyte colony stimulating factor (G-CSF) injections and/or antimicrobial treatment, but due to the loss of bone marrow function in some patients and the unresponsiveness of microbes to antimicrobial treatments, these treatments often fail and lead to high rates of morbidity and mortality in patients.
A logical treatment for chemotherapy-induced neutropenia is neutrophil transfusion, unfortunately, there is no effective method for ex vivo expansion of neutrophils for clinical use. Identifying an adequate source and number of expanded neutrophils are the main hurdles for using neutrophil transfusion as a means of treating neutropenia. A potential source for the production of neutrophils is cord blood. Cord blood CD34+ hematopoietic stem cells (HSC) make a reliable source of autologous neutrophils due to their ease of collection, less stringent HLA matching, and high rate of proliferation.
In an article published in PLOS ONE, Jie et al describes a four-stage culture approach for the large-scale ex vivo production of neutrophils for clinical use using cord blood CD34+ HSCs. Each culture stage was optimized for the appropriate combination of cytokines and growth factors to aid in expansion (stage 1) and differentiation (stage 2) of HSCs and expansion (stage 3) and further amplification (stage 4) of neutrophils. In addition, a rolling bottle culture system was tested along with varying speeds of rotation. High rotational speeds increased nutrition to the cells, aiding in cell growth. As for functionality, neutrophils derived from cultured cord blood CD34+ HSCs were fully functional as they exhibited chemotactic and bacterial killing effects similar to those of fresh peripheral blood neutrophils. Additionally, cord blood neutrophils survived longer in NOD/SCID mice as compared to peripheral blood neutrophils suggesting that they continue to mature in vivo providing possible long-term support.
Taken together, the authors’ new culture system produced 5 times higher volume of functional neutrophils than any other reported method generating 2.4×1011 neutrophils from a single cord blood unit. Given that each dose per donor is 2×1010neutrophils, this new method would provide a substantial number of neutrophils to treat neutropenia. Furthermore, the rolling bottle culture system along with medium modifications at each stage of neutrophil development decreased the cost of production. These findings provide a cost-effective treatment for chemotherapy-induced neutropenia, which would reduce the high risk of bacterial or fungal infection in patients.