Immunization does not interfere with uptake and transport by motor neurons of the binding fragment of tetanus toxin

Abstract

The nontoxic binding domain of tetanus toxin (fragment C or TTC) readily undergoes retrograde axonal transport from an intramuscular injection site. This property has led to investigation of TTC as a possible vector for delivering therapeutic proteins to motor neurons. However, the vast majority of individuals in the developed world have been vaccinated with tetanus toxoid and have circulating antitetanus antibodies that cross-react with TTC and may block the delivery of a TTC-linked therapeutic protein. However, it is uncertain whether the immune response is capable of completely neutralizing an intramuscular depot of protein prior to its internalization by presynaptic nerve terminals, where it is inaccessible to antibody. We have evaluated uptake of rhodamine-labeled TTC following intramuscular injection in normal animals and animals vaccinated with tetanus toxoid prior to injection of fluorescently labeled TTC. All animals demonstrated uptake of TTC, with fluorescence appropriately localized to the hypoglossal nerve and nucleus. The distribution and intensity of fluorescence within neurons and processes were indistinguishable between the two groups and were characteristic of TTC. Vaccinated animals showed levels of uptake of TTC into the brain comparable to those of immunologically naïve animals as measured by quantitative fluorimetry. All vaccinated animals had protective levels of antitetanus antibodies as measured by ELISA. Uptake of TTC by nerve terminals from an intramuscular depot is an avid and rapid process and is not blocked by vaccination associated with protection from tetanus toxin.

Tetanus Toxin Fragment C: Structure, Drug Discovery Research and Production

“…This allowed a small part of TTFC to be internalized and to reach the MN. Results have shown that vaccinated and unvaccinated animals presented detectable retrograde transport of TTFC using fluorimetry [72]. This demonstrated that at a high dose, TTFC could be used as a carrier for delivery of bioactive molecules into CNS even in vaccinated individuals.…”

“…Because TTFC contains many epitopes, its use as a carrier to deliver molecules to the CNS may be delicate in vaccinated individuals. Studies have been conducted to analyze the immunogenic side effects of the administration of TTFC in vaccinated animals [72]. They revealed that the amount of injected TTFC as a carrier (molar equivalent) generally exceeds 10,000 times the lethal dose of TT in a mouse model, and neutralization of all the TTFC injected was unlikely even for a vaccinated animal.…”

Imaging Net Retrograde Axonal Transport In Vivo: A Physiological Biomarker

“…However, a potential hurdle to consider in moving this to the clinic is the presence of neutralizing antibodies in the sera of most individuals in North America and Europe, a consequence of widespread tetanus vaccination. To ascertain whether tetanus vaccination affects retrograde uptake of TTC, Fishman et al quantified transported rhodamine‐labeled TTC in the hypoglossal with TT 52 . Despite elevated titers of antibody against TTC in the vaccinated animals, the net uptake of TTC in the hypoglossal nucleus was readily detected and not reduced by vaccination.…”

Tetanus Toxin C-Fragment: The Courier and the Cure?

“…Most individuals in the developed world are vaccinated against tetanus, and even for those that are not, treatments in humans are expected to be long term when natural immunogenicity of TTC may become a problem. However, uptake of TTC by nerve terminals from an intramuscular depot is rapid and is not blocked by immunization against tetanus toxoid in mice [113]. Rapid neural internalization may protect TTC and conjugated passenger molecules by making them inaccessible to the antibodies.…”