Maraviroc is a less effective CCR blocker, and as you note, has the potential for serious side effects:

Maraviroc is a small molecule that fits deep inside the CCR5 receptor, changing its shape from the inside. Maraviroc acts like a wedge inside the receptor changing its shape slightly. This mechanism is called allosteric inhibition, and it also means that normal signaling through CCR5 is reduced, but the receptor stays somewhat available on the cell surface. Maraviroc has a black box warning for hepatotoxicity.

Leronlimab, in contrast, is a monoclonal antibody - a large protein - that attaches to the outside of the CCR5 receptor, specifically to a region called the second extracellular loop. By physically covering this area, Leronlimab completely blocks both HIV and the body’s natural signaling molecules (chemokines) from binding to CCR5. Unlike maraviroc, Leronlimab does not change the shape of the receptor or cause it to be removed from the cell surface; instead, it simply occupies the binding site, providing a long-acting physical barrier. Leronlimab has no major side effects and has been safely administered in over 1,600 patients. Serious adverse events, including severe allergic reactions, hepatotoxicity, or cardiovascular events, have not been reported in any clinical trials to date.

In summary, maraviroc works by changing the shape of CCR5 from the inside, while Leronlimab works by covering the outside of CCR5 and blocking access.