NEW YORK, Aug 7 (Reuters) - MSCI said on Thursday it will add 42 securities and delete 56 from its widely followed ACWI equity index .MIWD00000PUS.

The three largest companies by market cap to be added to the developed markets index .WORLD are Rocket Lab Corp RKLB.O, Sofi Technologies SOFI.O and Affirm Holdings AFRM.O, all headquartered in the United States.

The three largest companies to be added to the emerging markets index .MSCIEF are China Citic Bank, Dian Swastatika Sentosa DSSA.JKand Laopu Gold 6181.HK.

All changes will be made as of the close of August 26, MSCI said.

(Reporting by Rodrigo Campos in New York; Editing by Leslie Adler)

((rodrigo.campos@reuters.com))