A cysteine modified anti-CD79b antibody comprising one or more free cysteine amino acids and comprising the following HVR sequences: (i) HVR-L1 comprising the sequence A1-A15, wherein AI-A15 is KASQSVDYEGDSFLN (ii) HVR-L2 comprising the sequence B1-B7, in which B1-B7 is AASNLES (iii) HVR-L3 comprising the sequence C1-C9, wherein C1-C9 is QQSNEDPLT (iv) HVR-H1 comprising the sequence D1-D10, in which D1-D10 is GYTFSSYWIE (v) HVR-H2 comprising the sequence E1-E18, in which E1-E18 is GEILPGGGDTNYNEIFKG (vi) HVR-H3 comprising the sequence F1-F10, in the one that F1-F10 is TRRVPIRLDY； wherein the antibody binds to the same epitope as a monoclonal antibody comprising the variable domains of SEQ ID NO and 10 SEQ ID No 14, an antibody comprising the variable domains of SEQ ID NO 207 and SEQ ID NO 208, or an antibody comprising the light chain sequence of SEQ ID NO 307 and the heavy chain sequence of SEQ ID NO 308； and wherein said one or more free cysteine amino acids are present in one or more selected regions of L10-L20, L105-L115, L109-L119, L116-L126, L122-L132, L163-L173 or L200-L210 of the chain light, or H1-H10, H18-H28, H79-H89, H107-H117, H109-H119, H111-H121, H270-H280, H366-H376 or H391-H401 of the heavy chain, in which said numbering is of according to the Kabat numbering system.Un anticuerpo anti-CD79b modificado con cisteína que comprende uno o más aminoácidos de cisteína libres y que comprende las siguientes secuencias HVR: (i) HVR-L1 que comprende la secuencia A1-A15, en la que AI-A15 es KASQSVDYEGDSFLN (ii) HVR-L2 que comprende la secuencia B1-B7, en la que B1-B7 es AASNLES (iii) HVR-L3 que comprende la secuencia C1-C9, en la que C1-C9 es QQSNEDPLT (iv) HVR-H1 que comprende la secuencia D1-D10, en la que D1-D10 es GYTFSSYWIE (v) HVR-H2 que comprende la secuencia E1-E18, en la que E1-E18 es GEILPGGGDTNYNEIFKG (vi) HVR-H3 que comprende la secuencia F1-F10, en la que F1-F10 es TRRVPIRLDY； en donde el anticuerpo se une al mismo epítopo que un anticuerpo monoclo
