The maker of the experimental COVID-19 antibody drug administered to President Donald Trump said that tests showing antibodies to the virus in his system may have only detected the residual effects of the drug itself, contradicting the commander-in-chief’s physician. Trump’s doctor, Sean Conley, said in a Tuesday memo that the president’s tests showed detectable levels of coronavirus antibodies, a sign he was healthy and fighting against the virus himself. Trump himself mused in a Monday video, “Maybe I’m immune.”

Regeneron, maker of the antiviral therapy REGN-COV2 given to the president, said otherwise in a statement to MSNBC Wednesday: “Most of the assays for IgG would not distinguish between endogenous (self-made) antibodies and ones delivered by our therapy. However, given the volume of IgG antibodies delivered in our therapy, and the timing of these tests, it is likely that the second test is detecting REGN-COV2 antibodies.” In reference to Conley’s memo, Dr. Seema Yasmin, an epidemiologist, tweeted, “Congratulations on detecting antibodies in someone on antibody treatment.”