DGAP-News: ABIVAX / Key word(s): Study results Abivax provides an update on the ABX464 clinical data and development strategy in ulcerative colitis 2021-09-14 / 18:00 The issuer is solely responsible for the content of this announcement.

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Abivax provides an update on the ABX464 clinical data and development strategy in ulcerative colitis . Excellent once-daily oral ABX464 efficacy and safety data in the phase 2b clinical trial in ulcerativecolitis (UC) patients, previously reported at 8-weeks, are further improved at . 16-weeks . Additional analyses (incl. miR-124 levels, histopathology, quality of life, etc.) underpin the potentialof ABX464 to become a safe short- and long-term efficient treatment option in UC . Novel and highly differentiated mechanism of action of ABX464 confirmed, showing specific upregulation ofa single microRNA, miR-124 . Additional long-term data of the ABX464 phase 2a open-label maintenance study in UC confirm the goodsafety and potent efficacy of ABX464 after 3 years of continuous chronic treatment . For the launch of its phase 3 program in UC, Abivax is getting ready for the mandatory consultations withthe regulatory authorities, starting with feedback from the US regulatory agency (FDA) expected by year end . Abivax' late breaking abstract on the phase 2b data in UC was selected for oral presenta-tion during UEGWeek Virtual 2021 (Monday, October 4). The data will be presented by the study's principal investigator, Prof.Séverine Vermeire, M.D., Ph.D. . Also, on the same day at UEG Week Virtual 2021, Abivax will host a Live Industry Symposium withpresentations by key opinion leaders Prof. Bruce Sands, M.D., M.S. and Prof. William Sandborn, M.D.

PARIS, France, September 14, 2021 - 6:00 pm (CEST) - Abivax SA (Euronext Paris: FR0012333284 - ABVX), a clinical-stage biotechnology company developing novel therapies that modulate the immune system to treat chronic inflammatory diseases, viral infections, and cancer, today provides an update on its clinical development strategy of lead compound ABX464 in UC and releases complementary data supporting the recently announced positive phase 2b top-line results. According to the latest additional analysis, the results after 16 weeks of once-daily oral treatment with ABX464 confirm and further extend the data with respect to the efficacy and the good safety profile already observed after 8-weeks of induction treatment.

Prof. Séverine Vermeire, M.D., Ph.D., Head of the IBD Center at the University Hospitals Leuven, Belgium, and principal investigator of the study, said: "These new data add to the promising outcomes of our ABX464 phase 2b study in UC, communicated in May this year. The consistency observed between the 8- and 16- week data is very reassuring in terms of the sustainability of the positive efficacy and the tolerability of ABX464, which is further strengthened by the very encouraging 3-year maintenance data of the phase 2a maintenance study. We are very excited to focus now on the implementation of the global phase 3 program in UC for the treatment of patients suffering from this debilitating disease, still in need for novel safe and long-term effective therapeutic management options."

Prof. Hartmut J. Ehrlich, M.D., CEO of Abivax, added: "In addition to its convenient once-daily oral administration, its fast onset of action, durable and maintained efficacy and good safety profile, the recent data analysis once again demonstrated the unique and novel mechanism of action of ABX464. This mechanism of action fundamentally differentiates this first in-class small molecule from any other drug or drug-candidate in the inflammatory field. At present, Abivax is preparing the upcoming consultations with the key regulatory agencies to discuss the phase 3 program in UC and the overall clinical development strategy of ABX464. We expect feedback from the FDA by the end of this year." Complementary data analysis of the ABX464 phase 2b induction clinical trial in UC

In May 2021, Abivax announced the top-line data of its ABX464 randomized, placebo-controlled phase 2b trial in UC after the 8-week induction treatment, which demonstrated significant clinical efficacy in the overall patient population, as well as in patients previously refractory to biologics and/or JAK inhibitors, on primary and key secondary endpoints and a good safety profile of ABX464.

The baseline disease characteristics were well balanced across all ABX464 dose groups and the placebo group. Enrolled patients suffered from longstanding UC with an overall median duration of 5.45 years. At inclusion, 71.4% of the patients showed a severe disease profile, with a baseline modified Mayo Score^[1] of 7 to 9 points. About 50% of the patients in each ABX464 treatment group and placebo were previously refractory to biologic treatments and/or JAK inhibitors. The majority of the patients was treated with concomitant UC medication at a stable dose (52% corticosteroids, 76.6% 5-ASA and 13.9% immunosuppressants).

At week 8, 35%, 40%, 44% of patients treated with 25mg, 50mg, 100mg respectively achieved endoscopic improvement compared to 14% in the placebo group. As per the clinical study protocol, only patients without an endoscopic improvement^[2] at week 8, had another endoscopy performed at week 16. This criterion was chosen for ethical reasons to not require an additional endoscopy for patients who already had an endoscopic improvement at week 8. Among the patients, who had another endoscopy at week 16, higher percentages of clinical remission^[3] were achieved at week 16 in the ABX464 treatments groups (25mg, 50mg and 100mg) with 15%, 20% and 23% respectively and 13% in the placebo group.

These results confirm the potency of ABX464 to maintain and to further improve clinical remission rates over time. Similar trends were observed for reduction of the modified Mayo Score, presence of clinical response^[4], and endoscopic improvement as well as reduction in fecal calprotectin in patients treated with ABX464 both in the entire population as well as in the subset of patients who were previously exposed refractory to biologic treatments and/or JAK inhibitors.

Complementary laboratory analysis at week 8 have now been completed, showing a highly statistically significant upregulation of the specific microRNA, miR-124, in rectal tissue in all patients treated with ABX464, compared to baseline. Increased miR-124 levels were observed in colorectal biopsies after 8 weeks of treatment with ABX464: The median increases were 13-fold for the 25mg group, 25-fold for the 50mg group and 25-fold for the 100mg group, while no upregulation was observed in the placebo group (1.02-fold increase), indicative of the positive pharmacological effect of ABX464.

Furthermore, a statistically significant reduction of the level of inflammation in the rectal tissue, assessed by the Robarts Histopathology Index (RHI), has been observed in UC patients treated with the lowest dose of 25mg ABX464 at week 8, compared to placebo (least square mean difference of 3.9 (7.3, 0.5) and p=0.03.

Importantly, the quality of life of patients treated with ABX464 showed a superior improvement at week 8 compared to the placebo group (40, 41 and 51-point improvement in 100/50/25mg compared to a 31-point improvement in the placebo). The "Health Related Quality of Life (HRQOL)" was measured from baseline using the standardized "Inflammatory Bowel Disease Questionnaire (IBDQ)" total score.

The pharmacokinetic (PK) data collected during this study confirmed the previous observation of dose-linearity and will allow Abivax to validate the population PK modelling approach, necessary for upcoming clinical studies and licensure.

Consistent with the other clinical studies, ABX464 was found to be safe and well tolerated at all dose levels during the 16-week induction period. Within the ABX464 phase 2b induction study, the most frequently reported adverse events were mild and transient (i.e. headache, nausea, gastrointestinal pain) and manageable with or without over-the-counter medication. Similarly, low rates of infections were observed in the active treatment groups (8.4%) compared to placebo (9.4%). No deaths or malignancies were reported in this study. In the ABX464 groups, serious adverse events (SAEs) occurred in 1.6% (25mg), 6.3% (50mg) and 6.2% (100mg) of patients and in 6.2% of patients in the placebo group.

These safety data are in line with what has been observed in more than 650 healthy volunteers and patients who have so far been treated in other clinical trials with ABX464 across different indications. New clinical data on the phase 2a maintenance study in UC

Separately, today, Abivax reports for the first time the 3-year efficacy data from its ongoing phase 2a maintenance study in UC. 15 out of the 22 patients who were initially enrolled into the phase 2a maintenance study in 2018, completed the third year of treatment with once-daily oral 50mg ABX464.

Among the 13 patients who underwent centrally read endoscopies at the completion of year 3, 11 patients (85%) were still in clinical remission, among which 7 patients (54%) had an endoscopic remission (endoscopic subscore=0) and 11 patients had an endoscopic improvement (endoscopic subscore=0 or 1).

The long-term safety profile of chronic ABX464 administration continues to be very favorable. Novel and unique mechanism of action of ABX464^[5],[6]

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September 14, 2021 12:00 ET (16:00 GMT)