By: Mary N. Wessling, Ph.D. ELS
Cross-Reacting Materials: The Motor Behind Conjugate Vaccines
Vaccines in history
The history and practice of vaccination as protection against viral infection is often thought to begin with Edward Jenner’s discovery that cowpox, a viral infection of cows, prevented smallpox in humans. However, it had long been suspected that survivors of smallpox seemed to be immune to further infection. Attempts to induce this immunity, referred to as variolation, had likely been practiced in Africa, Asia, and China, and only introduced to Europe in the 18th century.  Jenner, though, can certainly be credited for his scientific, experimental approach; his inoculation of an 8-year-old boy eventually was documented in his 1798 book An Inquiry into the Causes and Effects of the Variolae vaccinae. A disease discovered in the Western Counties of England . The number of lives that have been saved from misery and death is impossible to grasp; estimates of mortality from the disease before Jenner range between 30 and 35%.
What are carrier proteins, and why are they important in immunology?
Vaccines are often less effective in very young children whose immune systems are immature. For the past 35 years, vaccines have been “conjugated”—combined with a carrier protein –a cross-reactive material (CRM)–that enhances the immunogenicity of polysaccharide antigens.  The carrier protein CRM197 (Product #149), under consideration here, is a mutant version of Diphtheria toxin, in which the single amino acid exchange of a glycine in position 52 to a glutamic acid renders the protein non-toxic: it is one of the most widely used and highly effective carrier proteins . List Labs’ CRM197 has been used in a wide range of medical research, leading to a better understanding of the mechanism behind serious illnesses at all stages of the human life cycle. Most of the studies to date have employed animal models because direct research in humans would be ethically impossible.
Carrier protein CRM 197 could be used to protect premature infants from necrotizing colitis
Starting at the beginnings of life–necrotizing colitis (NEC) destroys the intestinal epithelium and is responsible for 20% to 50% of the mortality in premature infants, as well as causing significant long-term disability among its survivors. In an in vivo experiment using puppies exposed to NEC, Su et al (2013) used List’s CRM 197 as an antagonist to the epithelial protective E-cadherin/b-catenin complex. Their results suggest that administration of the heparin-binding epidermal-like growth factor could protect premature babies from developing NEC, and also that it could be used in treatment of diseases resulting in intestinal injury.
List Labs’ carrier protein used in Alzheimer’s research
A disease that causes misery at the other end of life, Alzheimer’s disease, is associated with amyloid plaques, specifically amyloid-beta, the subject of intense investigation. Vingtdeux et al (2016) in a murine study developed a novel vaccine against the pathologically relevant A-beta pE3 using List’s CRM197 as a carrier protein for epitope presentation.
CRM197 carrier protein impacts humans over a lifetime
In mid-life, three of the research applications of List Labs’ CRM 197 have potential for bringing health to human populations. First, heroin addiction: Jalah et al (2015) sought to develop a vaccine against heroin addiction, one that would block its biological effects by sequestering the drug in the blood, preventing it from crossing the brain barrier. The researchers used List’s CRM197 along with a heroin/morphine hapten conjugate of previously established efficacy to improve its antinociceptive effects.
Another life-shortening threat, diabetic nephropathy is, in 40% of all cases, the leading cause of end-stage kidney disease. You et al (2013) injected CRM 197 in mice for 6 weeks to investigate the mechanism whereby the podocytes (cells in the Bowman’s capsule that filter the blood, foot-shaped, ergo podo…) are injured. The culprit was identified as the proinflammatory M1 subset of macrophages; finding a way to attenuate the effect of the M1 macrophages on the podocytes suggests a new therapeutic approach.
And a final example: Human disease can be caused by contamination of milk products by aflatoxins—certainly a life-long concern. Researchers immunized Holstein Friesian heifers with an experimental vaccine based on the immunogen anaflatoxin B1 AnAFB1] . They then studied the response to AnAFB1 conjugated with List Labs CRM197 carrier proteins to determine the efficacy of inducing antibodies specific to AFB1.
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