Factory farmed antibodies secreted from cloned B-Cells, or injecting modified cells in mice to grow tumors that secrete the antibodies in a fluid, theres slightly different methods but they generally seem to fall along those 2 lines.
It's the Regeneron treatment, REGN-COV2, based on the initial study results, it would of reduced the severity (viral load) of Trump's infection to a minimum of 1% and a maximum of 50%, and would of reduced his infection time to just over half.
Here's the investor report & first trial results that came out a couple days before Trumps diagnosis. It's what Trump was referring to when he talked about miracle treatments, it's consistently catastrophic for the virus and manages to compensate for both high viral loads and weak immune systems, so it should be able to bail anyone out of a corona death.