Question Number: 173
PDR Number: SQ22-000542
Date Submitted: 21/11/2022
Department or Body: Department of Health
66. The biodistribution and fate of lipid nanoparticles (LNP) were studied in animals and in vitro. The distribution of lipid nanoparticles encapsulating mRNA encoding luciferase was investigated by monitoring a radiolabelled lipid-marker in rats. The major uptake of this lipid-marker was noted at the injection site and in the liver, with lower levels distributed to the spleen, adrenal glands and ovaries. The LNP dose in the distribution study was considerably higher than the human dose on a µg/kg body weight basis. Therefore, much less LNPs would be found in the tissues in humans after vaccination. In addition, radioactivity (lipid-marker), not the actual lipid in the vaccine, was measured in the rat study. The detected radioactivity could represent smaller pieces of the lipid in the vaccine. It is a common practice to measure radioactivity in radio-labelled tissue distribution studies for pharmaceuticals because of the high sensitivity of radioactivity measurements and the difficulty of detecting pharmaceuticals per se in tissues. The lipid-marker was detected in ovaries in the rat study. Importantly, fertility was unaffected in nonclinical studies in animals receiving vaccine doses up to 200 times the human dose in reproductive and developmental toxicity studies. Microscopic examination showed no changes in organs including the ovaries from repeat dose toxicity studies in animals after they received repeated, high doses of the vaccines.
67. In addition to the pharmacokinetic and biodistribution studies to determine where the mRNA vaccine lipids may be distributed in the body, repeat dose nonclinical studies were conducted to investigate potential toxicity of the vaccine and LNPs. The test material in the animal studies was identical to the final clinical vaccine formulation as administered to patients. The findings from the animal toxicology studies were consistent with expected immune responses (including inflammation at the injection site and hypercellularity of lymphoid tissues). There were no effects on ovaries or other organs except the lymphoid tissues (desired immune responses) and mild vacuolation in liver cells (most likely related to lipid uptake). Vacuolation of liver cells was completely reversible three weeks after the last vaccine dose.
68. The biodistribution of the mRNA and expressed antigen encoded by the mRNA component of the vaccine was expected to be dependent on the LNP distribution. To visualise the tissue distribution of the mRNA-LNP formulation, mRNA encoding luciferase was formulated in an LNP formulation identical to the Pfizer BNT162b2 vaccine. Following an intramuscular (IM) injection of the luciferase mRNA formulation in mice, luciferase was detected by whole body imaging mainly at the injection site, which declined to the background level after 9 days. Luciferase was also seen in the liver, which disappeared in 48 hours. Very low levels of mRNA or spike protein may be detectable for a longer period. However, animal toxicity studies at very high vaccine doses raised no safety concerns.
69. Distribution studies are not typically conducted for an antigen (spike protein) or biological medicines, e.g. trastuzumab. See response to Question to 94 (SQ22-000555).
70. Animal studies showed that ALC-0159 (PEG-lipid, one component of the LNP) was completely eliminated in 14 days, while ALC-0315 (another lipid component) was detectable in the liver 14 days after the intravenous dose, but the level was significantly lower within 24 hours of dosing, indicating gradual elimination from the body. Repeat dose toxicity studies in rats with the Pfizer vaccine formulation with LNP doses approximately 100 times the human clinical dose showed no systemic toxicity. See also responses to Questions 66 and 67. 76. See response to Question 66.
