Tonix Pharmaceuticals Holding Corp. is looking to lessons from tuberculosis and smallpox to guide its future in infectious diseases. The company is developing an intradermal skin test like that used for TB to measure T-cell immunity to SARS-CoV-2, the virus that causes COVID-19. It also has three vaccines in development for COVID-19 that rely on horsepox, likely the form of vaccinia used by Edward Jenner to create the smallpox vaccine.

Shares of Chatham, N.J.-based Tonix rose 22% on news of the development of the TNX-2100 skin test. The company also reported a stock offering of approximately 58.3 million shares of common stock at $1.20 per share. The offering was expected to raise $70 million, before fees and expenses, which the company plans to use to fund further evaluation of the test, several vaccine candidates, and other clinical trials.

"We believe TNX-2100 has the potential to measure T-cell immunity to [SARS-]CoV-2 and therefore serve as an aid to COVID-19 diagnosis to support patient care, public health surveillance, and vaccine trials," said Tonix CEO Seth Lederman. The company has received written response from the U.S. FDA, which it characterized as “positive so far,” to a Type B pre-investigational new drug (IND) meeting package describing the diagnostic skin test, which measures the delayed-type hypersensitivity reaction to SARS-CoV-2.

“Based on guidance provided by FDA in their written response, we believe we have the information necessary to respond to queries and file the IND application in the second quarter of 2021,” said Herbert Harris, Ton’s executive vice president for translational medicine. The company expects to start trials of the test in the second half of 2021.

The importance of T-cell immunity

The new test could simplify measurement of T-cell immunity, which lasts considerably longer than antibody-based immunity. While antibodies to many viral diseases wanes in six months or so, T-cell immunity for some infections lasts a lifetime. Notably, the level of antibody response in individuals known to have been infected with SARS-CoV-2 and recovered varies from quite robust to undetectable. A T-cell test would illuminate the nature of immune responses, particularly in people without discernable antibodies.

Currently, no standardized laboratory tests measure T-cell immune response to the novel coronavirus and the ones available “using intracellular cytokine staining are only done in advanced, highly specialized labs,” Lederman told BioWorld. “Those tests can’t be standardized ... but they have shown us that T-cell immunity is important and that people with strong T-cell response are less likely to go to the hospital.” In comparison, the highest levels of neutralizing antibodies are found in patients who die on respirators, he noted.

The test could be useful as a biomarker for immunity and to stratify participants in vaccine trials, so that individuals who started with some natural immunity based on previous infection are not included in analyses with people who had no immunity prior to vaccination. In addition, the test would help measure response to vaccination and assess durability of protection.

“The skin test could be used after vaccinations to see if they were successful. If someone didn’t have a good response, you would revaccinate,” Lederman said.

If trials support the test, it could be used by clinicians, patients, employers, long-term care facilities and public health officials to confirm immunity to SARS-CoV-2 quickly and inexpensively. Given that the durability of the vaccines currently approved and in development are unknown because the virus has only been identified for just over a year, a reliable and rapid way to test persistence of immunity will be a tool for vaccine developers and protection of public health.

The test

The Tonix skin test for T-cell immunity would work like the Mantoux test for TB, pictured here. Credit: Wikimedia

TNX-2100 uses a procedure similar to the Mantoux purified protein derivative test for tuberculosis. A small amount of an antigen is inserted intradermally on the underside of the forearm with a tiny needle. Within 48 hours, individuals with T-cell memory develop hard red, raised lesions that can be measured with a take-home device.

The Tonix test uses three synthetic peptides (TNX-2110, TNX-2120, and TNX-2130) that correlate to different protein components of SARS-CoV-2. TNX-2110 represents multiple proteins from the virus, while TNX-2120 represents the spike protein and TNX-2130 non-spike proteins. Each of the three synthetic peptides would be injected in a different part of the arm. Individuals exposed to or infected by SARS-CoV-2 would be expected to develop a red wheal in all three locations. Someone successfully immunized with one of the current vaccines, but not previously exposed, would see a reaction only to TNX-2120 as those vaccine only encode the spike protein. The diameter of the lesion indicates the amount of T-cell immunity to the test peptides.

“It takes the whole parameter of T-cell immunity out of specialized labs,” Lederman explained. “The test can be administered by trained individuals less skilled than a nurse and patients can take a picture on their phone showing the size of the lesion with a paper ruler.”