Whole parasite vaccines for the asexual blood stages of Plasmodium

After many decades of research, an effective vaccine for malaria is still not available. Most research efforts have focused on identifying a key target antigen and then using powerful adjuvants to generate specific antibodies that can block parasites from entering host cells (hepatocytes, red blood cells). However, the inability to generate sufficiently potent antibody responses has led to significant disappointment with current vaccine programs. An additional challenge for sub-unit vaccines is that key vaccine antigens are highly polymorphic. These challenges have spurred radically different approaches to malaria vaccine development. Many of these involve the use of “whole parasites”—either extracted from mosquitoes or cultured. With these, every parasite molecule for that particular strain is included in the vaccine. This strategy is showing great promise following several clinical trials with irradiated sporozoites. However, a whole-parasite approach to a blood stage vaccine has not advanced as quickly. This article outlines the history, the different approaches that are being taken and the challenges associated with whole parasite blood stage vaccines and discusses recent exciting developments as these vaccines now move into the clinic.