Does monoclonal b-cell lymphocytosis make the patient more vulnerable to infections, e.g., hypostatic pneumonia? is monoclonal b-cell lymphocytosis capable of transforming into acute leukemia?

Still not well known: This is a newly recognized entity, so there is not much known about it. It is likely a precursor of chronic lymphocytic leukemia(cll) which as you know can stay in this stable indolent phase for many years. That is what you need to hope for. Unless it progresses, you do not need to worry about it for a long time.

No infections in MBL: The definition of mbl is an elevated lymphocyte count with a lack of symptoms or complications. It can transform into cll (chronic lymphocytic leukemia), in which low immunoglobulins and the abnormal b lymphocytes can indeed cause increased infections. Neither of these has been associated with transformation to acute leukemia, although cll can become an aggressive lymphoma.